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Structural and interactive relationships between intertidal Fucus populations and associated faunal assemblages Nassichuk, M. D. 1975

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STRUCTURAL AND INTERACTIVE RELATIONSHIPS BETWEEN INTERTIDAL FUCUS POPULATIONS AND ASSOCIATED FAUNAL ASSEMBLAGES  by  Michael David Nassichuk B.Sc., University of B.C., 1972  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in the Department of Botany  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA February, 1975  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia,  I agree that  the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It is understood that copying or publication  of this thesis for financial gain shall not be allowed without my written permission.  Botany  Department of  The University of British Columbia Vancouver 8, Canada  Date  March  ,  1975  1  ABSTRACT  Intertidal populations of Fucus at two sites along the British Columbia coast were investigated in an attempt to establish relation ships between various structural components of the alga and associated faunal assemblages.  Experimental field and laboratory techniques  were utilized along with a sampling program designed to monitor temporal variation in faunal diversity and to determine the role of algal complexity in the formation and maintenance of associated animal communities. Algal structure was shown to be correlated with faunal diversity although other factors, i.e., Fucus height diversity, were more strongly associated with faunal diversity at certain times of the year.  The  diversity of the fauna associated with Fucus differed between the two study areas and possible reasons for the differences are discussed. The factors controlling the lower intertidal distribution of Fucus were examined through field and laboratory experimentation.  Biological  interactions appear to be of primary importance in controlling the lower distribution of the alga.  11  TABLE OF CONTENTS Page Abstract  i  List of Figures List of Tables  vii  Acknowledgements  viii  INTRODUCTION  1  (a)  General  1  (b)  Selected aspects of the biology of Fucus  4  MATERIAL AND METHODS  6  (a)  Description of study areas  6  (b)  Data analysis methods  8  Cc)  Bowen Island sampling techniques  10  Cd)  Fucus transplantation experiments  12  Ce)  Transplantation of structurally variable plants  13  (f)  Fucus density effects  13  (g)  Littorinid and limpet growth experiments  14  (h)  Fucus growth measurements  15  Ci)  Investigations of factors affecting the lower intertidal limits of Fucus  15  (I)  15  (II) (III)  Pisaster—mediated mortality Hermit crab grazing Balanus—Fucus competition  16 17  (j)  Lighthouse Park sampling techniques  17  (k)  Mytilus edulis—Fucus competition  17  (1)  Limpet marking experiments  18  Cm)  Laboratéry experiments  19  (I)  19  Littorina and Acmaea behavior experiments  111  Idothea selection experiments  (II)  20  (III)  Pagurus grazing experiment  20  (IV)  Pisaster—Fucus interactions  21  CV)  Detachment of Fucus by Nytilus  21 22  RESULTS (a)  Bowen Island and Lighthouse Park Fucus population characteristics  22  (1,)  Bowen Island sampling  23  (c)  Fucus transplantation results  27  (d)  Density transplants  28  Ce)  Littorina and Acmaea growth experiments  30  (f)  Factors affecting the lower intertidal limits of Fucus  30  (g)  Hermit crab grazing  31  (h)  Balanus—Fucus competion  32  Ci)  Plant growth studies  32  (j)  Lighthouse Park sampling  34  (k)  Mytilus—Fucus competition (Juvenile Plants)  34  (1)  Mytilus—Fucus competition (Adult Plants)  37  (m)  Limpet marking experiment  38  (n)  Laboratory experimentation  39  (I)  Behavior experiments Idothea selection experiments  (II)  Pagurus grazing  (III)  Pisaster—Fucus interactions  (IV) (V)  Mytilus removal of Fucus  DISCUSSION  39 39 40 41 41 42  (a)  Diversity and community structure  42  (b)  Lower intertidal distribution of Fucus  51  (c)  Fucus characteristics at Bowen Island and Lighthouse Park  53  iv SUNMARY  54  LITERATURE CITED  55  FIGURES  60  APPENDIX  128  TABLES  129  V  LIST OF FIGURES Page  Figure 1.  Map of Bowen Island showing study area.  61  2.  Map of Point Atkinson showing study area at Lighthouse Park.  63  3.  Fucus attachment to cement block.  65  4.  Cages used in littorinid and limpet growth experiments.  67  5.  Experimental apparatus used in laboratory experiments.  69  6.  Frequency distribution of plant heights.  71  7.  Frequency distribution of number of dichotomies per plant.  73  8.  Regression of Fucus height against number of dichotomies.  75  9.  Photographs of Fucus from Bowen Island.  77  10.  Diagram of Fucus with associated invertebrates.  79  11.  Changes in the number of L. sitkana over time.  81  12.  Changes in the number of L. scutulata over time.  83  13.  Changes in the number of M. edulis over time.  85  14.  Changes in the number of amphipods over time.  87  15.  Change in mean species diversity and Fucus height diversity over time.  89  16.  Changes in the mean number of animals on Fucus over time.  91  17.  Regression of species diversity against Fucus height diversity.  93  18.  Frequency distribution of numbers of L. sitkana.  95  19.  Frequency distribution of numbers. of H. plumulosa.  97  20.  Frequency distribution of numbers of N. edulis.  99  vi Figure  Page  21.  Change in mean species diversity of the substrate fauna.  101  22.  Changes in mean species diversity of structurally different plants.  103  23.  Changes in mean species diversity for groups of plants.  105  24.  Changes in mean number of organisms on transplanted groups of plants.  107  25.  Regression of limpet length against limpet height.  109  26.  General pattern of Fucus zonation on Bowen Island.  111  27.  Pagurus—grazed Fucus.  113  28.  Regression of Fucus height against growing time.  115  29.  Growth and dichotomization of Fucus.  117  30.  Idothea grazing on Fucus.  119  31.  Changes in mean species diversity and Fucus height diversity.  121  32.  Frequency distribution of M. edulis.  123  33.  Mean growth rate of plants cleared of Mytilus and plants with intact Mytilus.  125  34.  Selection of Fucus by Idothea.  127  vii  LIST OF TABLES  Table  Page  1.  Comparison of structural characteristics of Fucus between Bowen Island and Lighthouse Park.  129  2.  Organisms found on Fucus and on the substrate under Fucus.  130  3.  Relationships between independent and dependent variables for Bowen Island and Lighthouse Park, seasonal data pooled.  131  4.  Relationships between independent and dependent variables for Bowen Island on a seasonal basis.  132  5.  Comparison of final heights of Littorina sitkana.  134  6.  Comparison of final heights of mature plants transplanted to three intertidal sites.  135  7.  Relationships between independent and dependent variables for Lighthouse Park on a seasonal basis.  136  8.  Comparison of number of A. pelta remaining on cleared and uncleared areas.  137  9.  Comparison of number of L. sitkana and L. scutulata found on Fucus and non—Fucus sides of laboratory tank.  138  10.  Selection of structurally variable plants by Idothea wosnesenski.  139  viii  Acknowledgements  I thank my supervisor, Dr. Ron Foreman, for his continued support throughout all phases of the work leading to this thesis and for attempting to teach me some Botany.  In particular his advice,  criticisms, and financial support are greatly appreciated. To Dr. Robin Harger I give a heartfelt thanks for his constructive comments and suggestions prior to the initiation of this study.  Robin also critically read the original manuscript.  I want to thank Susan Latimer who cheerfully assisted me in the field and devoted some time towards preparing some of the figures in this thesis. Thanks also to Dr. Sylvia Behrens who kindly read the original manuscript and to Julie Celestino who identified some of the algae. Several individuals at the Canadian Oceanographic Identification Centre in Ottawa assisted with invertebrate identification, in particular, J. A. Fournier, R. M. O’Clair (polychaetes), and E. L. Bousfield (amphipods).  1  INTRODUCTION  a)  General  The functional role of marine benthic algae in nearshore communities has been the subject of an increasing number of investigations.  The importance of marine algae to marine animals has  been recognized for some time (Scagel, 1959) but the dynamics of the interactions between plants and animals remains largely unknown. Recent work by Mann (1972, 1973) has elucidated the significance of benthic macrophytes as primary producers.  Few intertidal investigations have been directed at assessing interrelationships between algal populations and associated animal assemblages.  One such study (Glynn, 1965) consisted of an examination  of species interrelationships of rocky intertidal Balanus glandula— Endocladia muricata associations.  Paine (1971) experimentally  determined that mussels on a stretch of New Zealand coastline were limited in their lower intertidal distribution through the actions of a large brown alga, Durvillea.  A number of attempts have been made to interpret associations between certain terrestrial faunal communities and the structure of the presiding vegetation.  MacArthur (1965) describes a relationship between  bird species diversity and a measure of vegetation complexity, foliage height diversity, for North American bird populations.  Over a wide  geographical area bird species diversity could be predicted from knowledge of the foliage height diversity.  Pianka (1967) established correlations  between the structural complexity of desert vegetation, plant volume  2 diversity (a measure of the volume of space occupied by a particular plant) and lizard species diversity.  Speculation as to which aspect of  vegetation diversity, i.e., plant structural diversity or plant species diversity, is the more important in determining animal species diversity has been raised (Murdoch, Evans, and Peterson, 1972) and remains unanswered.  This study is, in part, an attempt to analyze the relationship between the structural complexity of a common intertidal alga, Fucus, and its resident faunal assemblage.  Jones (1948) examined interactions  between fucoids and the limpet Patella in an experimental study designed to determine the role of invertebrates in affecting intertidal algal distributions.  Jones determined that there was  “...  an ecological  balance between Patella and algae of the shore” where grazing by Patella controls the distribution of Fucus.  The succession of algae on intertidal  shores in the absence of limpets was followed by Lodge (1948) who noted an expansion of the zone occupied by Fucus vesiculosus in the absence of limpets.  The dynamic balance between limpets and Fucus has been  illustrated as a cyclic relationship (Southward, 1964) where an increase in limpet settlement can decrease fucoid populations and a decline in limpets increases the survival rate of newly settled plants thereby increasing the size of the overall Fucus population.  The animal populations associated with Fucus have been studied, primarily in a qualitative fashion, by a few European researchers. Colman (1939) examined the invertebrate fauna of eight species of inter— tidal algae including three Fucus species, F. spiralis, F. vesiculosus, and F. serratus.  In total, 177 animal species were found with copepods,  3  acarines and littorinids dominating in numbers.  Later, Wieser (1952)  investigated the microfauna of certain intertidal algal species and Hagerinan (1966) quantitatively analyzed the fluctuations in animal numbers associated with F. serratus growing sublittoraly.  Experimental  manipulative techniques were applied by Haage and Jansson (1970) who quantified changes in animal numbers occurring in F. vesiculosus belts. Inter— and intraspecific competition among epiphytes on fronds of F. serratus is described by Stebbing (1973). A second major aspect of this study consists of an examination of the factors affecting the lower intertidal distribution of Fucus. Intertidal ecologists have long been concerned with identifying the important factors which limit the vertical distribution of both plants and animals.  Recently the importance of biological interactions in  determining the lower limits of intertidal distributions has been reviewed (Connell, 1972).  Those biological processes which are of primary  importance have been identified from field experimentation, namely predation (Paine, 1966, 1974; 1961a, b;  Harger, 1970, 1972;  Connell, 1970) and competition (Connell, Dayton, 1971).  The prevailing attitudes  towards intertidal zonation and seaweed distributions have been examined by Chapman (1973) who concludes that biological interactions are of primary importance in the lower intertidal zone.  For example, competition  between Fucus spiralis, F vesiculosus, and F serrätus on British shores is cited as the major process leading to distinct bands of the three species.  I have combined field and laboratory experiments in an attempt  to delineate those processes affecting the local intertidal distribution of Fucus.  4  b)  Selected Aspects of the Biology of Fucus  The genus Fucus is in the order Fucales, class Phaeophyceae. Distinguishing features of this order include discoid holdfasts, apical growth via apical cells and antheridia and archegonia located on conceptacles (Fritsch, 1945).  Eggs and sperm are discharged in packets  of 8 and 64 respectively with each packet enclosed by a inembranous sheath.  Fertilization occurs after gametes are released from the  conceptacles and the eggs are free and the sperm motile (Pollock, 1969). Laboratory studies of east coast F. distichus showed that fertilization occurred primarily within the conceptacle (McLachlan, Chen and Edelstein, 1971).  I found embryos in the conceptacles of mature plants from  Bowen Island which suggests that some fertilization occurs within the conceptacle.  Once fertilized the cell secretes a glue—like substance  which acts to adhere the eggs to the substrate.  Knight and Parke (1950)  found that fertilized eggs of F. serratus and F. vesiculosus were widely dispersed over the shore and became firmly attached to the substrate within a few hours.  Cell differentiation occurs rapidly with a rhizoidal  region being formed at the basal pole which subsequently develops into a holdfast and a thallus region develops from a thallus cell at the apical pole (Jaffe, 1968).  Species of the genus Fucus exhibit tremendous phenotypic plasticity.  The absolute number of species of Fucus remains a matter  of debate but estimates range from 6 to 15 species (Powell, 1963).  Dawson  (1961) lists only one species of Fucus as occurring on the Pacific coast of Canada and more recent publications (Widdowson, 1973) support this theory.  This species, F. distichus, has two sub—species, edentatus and  5 evanescens, with both forms being found along the Pacific coast. Distinction between the forms of Fucus is often difficult in light of the fact that F. distichus is  “...  apparently most polymorphic of all  on parts of the Pacific Coast of North Anterica...” (Powell, 1963). Recent investigations (Conway, 1974;  personal communication), suggest  that a second species, F. spiralis, may be present on the Pacific coast. In Canada this species was formerly thought to occur only on the Atlantic coast.  Pollock (1969) describes a diminutive form from the  San Juan Islands off the coast of Washington which he thought appeared similar to F. spiralis.  The Fucus community I encountered on  Bowen Island appears to consist of F. distichus, a form identified as F. spiralis by Dr. Conway, and perhaps a hybrid form (Conway, 1974; personal communication).  Burrows and Lodge (1951) discuss the problem  of Fucus hybrids and the extent to which they occur in nature.  The  Fucus of Lighthouse Park is of the F. distichus type with none of the  !  spiralis type.  Because of the taxonomic problems inherent in the  classification of Fucus I shall refer only to the genus Fucus throughout the remainder of this thesis as it pertains to my specific investigation.  6 MATERIAL AND METHODS  a)  Description of Study Areas Two major study areas were utilized for the examination of  Fucus—faunal associations.  The areas, Bowen Island and Lighthouse Park  on Point Atkinson, were chosen primarily because they differed in their degree of wave exposure.  Bowen Island is situated at the mouth of  Howe Sound (Figure 1) and Point Atkinson juts into the Strait of Georgia where it is bordered on either side by Burrard Inlet and Howe Sound (Figure 2). Graf ton Bay  The study sites of Bowen Island were situated near 9 4 V 4 ( 2 0  N. and 124°22’ W.) and are relatively well protected  by the prominence of Gambier and Keats Islands. 0  and 124 16  ,  Point Atkinson (49°20’ N.  W.), unlike the Bowen Island site, receives the bulk of the .  larger wind generated waves from the Strait of Georgia. The intertidal zone at Lighthouse Park is characterized primarily by steep granite cliffs and large bouldered beaches.  Salinity  and temperature measurements were not made during the course of this study. Such data were obtained from published oceanographic records of the Howe Sound and Burrard Inlet area.  Comprehensive oceanographic data off  Point Atkinson is not available so the values used are extracted from the oceanographic stations located closest to the study area.  These are  station Burr—3 (Institute of Oceanography, U.B.C., Data Report 34, 1972; 49°19.l’ N. and 123°12.1’ W.) and station 15 (Waldichuk, Markert, and Meikle, 1968;  49°19.30’ N. and 123°17.50’ W.).  Salinity values ranged  from a low of liZa to a high of 23%. over a ten year period from 1962 to 1972.  Temperature variation for the same period of time ranged from about  7 6°C to 18.5°C. The shorelines on Bowen Island range from steep cliffs to gently sloping sandy and pebble beaches.  The main study area consisted  of large and small bouldered beaches interspersed with large rock outcrops.  The closest oceanographic stations to the study area were  How—2 and How—2.5 (Institute of Oceanography, U.B.C., Data Reports 30 and 34;  49°23.3’ N. and 123°l7.8’ W.  123°16.0’ W. (How—2.5)). and Meikle, 1968;  (How—2) and 49°27.O’ N. and  Data from station 11—12 (Waldichuk, Markert,  49°25.20’ N. and 123°26.27’ W.) were also considered.  Temperature values between 1962 and 1972 ranged from 6.3°C and 18.7°C. Salinity values ranged from 12.35%. to 22.49%.. over the same time period. The two study areas, notwithstanding the paucity of oceanographic data, seem to be influenced by similar temperature and salinity regimes. Fucus is the numerically dominant intertidal alga at Bowen Island in terms of numbers of individual plants, biomass, and area covered.  The upper limits of Fucus coincide with the maximum upper  limits of Balanus glandula in most areas.  Rhodomela larix can be found  in adjacent tidepools and small crevices, and Prionitis lanceolata is common in the few small tidepools of the area.  Some Spongomorpha sp. and  Enteromorpha sp. also occur in scattered patches at certain times of the year. At Lighthouse Park, Fucus also tends to be the dominant alga in terms of abundance but the presence of many tidepools provides a habitat for a variety of other forms.  Laminaria saccharina and Alaria sp. are  quite common on rocks in the lower intertidal zone and in tidepools higher  8 in the intertidal region.  Other forms found during the investigation  are Microcladia coulteri, Prionitis lanceolata, Iridaea cordata and species of Enteromorpha, Ulva, Monostroma, Pylaieila, Rhodoglossum and Porphyra.  b)  The epiphyte, Elachistea fucicola, frequently grows on Fucus.  Data Analysis Methods The measurement of the diversity of an assemblage of  organisms ranges from simple enumeration of the species present in a collection to the indices based on information theory (Shannon, 1948). The index based on information theory, (H’), is a measure of the uncertainty of identification of an individual picked from a collection of individuals where, log 1 =  1:1  =  s  =  proportion of individual organisms represented by the th species. total number of species.  A second index (B) (Brillouin, 1962) measures the information content of a total collection of organisms where, bits of information  B  =  , 2 1og  N  =  total number of organisms  1 N  =  number of organisms of species 1  2 N  =  number of organisms of species 2  N  =  number of organisms of species s  ’ 2 N  NJj  9 The diversity per individual (H) Pielou, 1966) is obtained by dividing the expression for (B) by the total sample size:  H  =  ‘  log,  ...Ni1 !N 2  The index (H’), unlike (H), is not dependent on sample size and is used when the sample being analyzed contains all the species present in the parent population (Pielou, 1966).  Harger and Tustin (1973a) point out  that much confusion remains in the literature over the usage of (H’) and (H), and that both indices should be reported together to aid in comparisons with other investigations.  The application of diversity  measures as interpretive tools in the analysis of community structure has been questioned.  Hurlbert (1971) suggests that species diversity  has become a “meaningless concept” but his desire to abandon the concept of species diversity has been labelled “premature” by Hill (1973) and Harger and Tustin (1973b) suggest that Huribert’s species abundance ratios in lieu of diversity measures will not complement present under standing of community structure and function.  In this study both species  diversity (H’) and diversity per individual (H) have been presented together.  Measurement of diversity is not restricted to species composition but can be equally applied to other characteristics of communities and populations such as species biomass, height distributions etc.  I have applied information theory in analyzing the heights of  individual Fucus plants to obtain a measure of Fucus height diversity. Each plant was assigned a size class and classes were defined at 3 cm intervals.  For example, all plants 0—3 cm in height are in the first  10 category, those 3—6 cm in height are in the second category, and so on. The information formula (H’), is applied to the proportion of plants in each category to obtain the measure of Fucus height diversity.  c)  Bowen Island Sampling Techniques  An intertidal sampling program was initiated in May, 1973 and continued through July, 1974.  Vertical Line transects extending from  the uppermost limit of the Fucus zone to the lowest intertidal limit were utilized.  Sampling was performed using a 0.1 m 2 quadrat at approximately  1 meter intervals down the transect. sampling techniques were employed.  Two somewhat different Fucus  In one method the percentage of the  quadrat covered with Fucus was estimated visually and expressed as a percentage cover value.  Individual plants within the quadrat were removed  singly from the substrate by means of either a sharpened putty knife or with the use of forceps.  Each plant was searched for its associated  organisms and if any were found the distance each organism was situated from the plant holdfast was measured with a centimeter ruler.  Following  such measurements each plant along with those organisms found on it was placed in a labelled plastic bag.  Those plants on which no organisms were  found were placed collectively in a separate labelled bag.  The portion  of those plants overlapping the quadrat from outside was also collected. After all plants from the quadrat had been removed in this manner, the invertebrate fauna associated with the rock substrate within the quadrat was collected.  The slope of the substrate was then visually estimated  (e.g., 400) and also the type of substrate (e.g., pebble, boulder, etc.).  The second sampling method utilized was essentially similar to  11 the first except that the position of the animals on each plant was not determined;  rather, all plants and their associated fauna were  sampled collectively.  In this way a more rapid estimate of population  abundance could be determined. All samples collected were sorted in the laboratory. fauna of each individual plant was counted and recorded.  The  The maximum  height of each plant was obtained using a centimeter ruler.  A second  measurement, the total number of dichotomies which resulted in fronds greater than one centimeter in length, was determined for each plant. This measure arose from a need to have a comparable measure of individual plant complexity which could be used in assessing structural differences between plants from different areas.  Also it was thought  that such a measure would be a biologically important factor that could be related to animal community structure.  The wet weight of the Fucus  in each quadrat was determined once all the animals were removed.  The  plants were then dried in a drying oven at 105°C for 36 hours to assess dry weight.  For each quadrat the following measurements were recorded,  each of which became an independent variable in the multiple regression analysis which is discussed later.  1.  Total number of plants.  2.  Total cumulative height of all plants.  3.  Total number of dichotomies.  4.  Mean height per plant.  5.  Mean number of dichotomies per plant.  6.  Ratio of total number of dichotomies to total height.  7.  Wet weight of Fucus.  12 8.  Dry weight of Fucus.  9.  Cover value  (%).  10.  Distance along intertidal transect.  11.  Fucus height diversity.  Fucus Transplantation Experiments  d)  Experimental manipulation of intertidal algae is a difficult Descriptions of methods used are sparse for most intertidal forms  task.  except for techniques utilizing the transplantation of algal covered boulders to various parts of the intertidal zone (Pollock, 1969) and the transplantation of large kelps such as Macrocystis (North, 1964; 1972) in the subtidal zone.  Pace,  Waaland (1973) developed a simple technique  using polyethylene clamps to transplant species of Iridaea and Gigartina to different depths in growth experiments.  A new technique for the  present experimental program which involved transplantation of individual Fucus plants onto replicate cement blocks was devised.  Considerable time  was spent in experimenting with a variety of possible techniques prior to choosing the method used which is as follows:  ¼  An electric drill with a  inch drill bit was used to drill a 2 inch deep hole into a cement block.  Experimental plants were scraped from the substrate with their holdfasts intact. O.D.  ¼  A  ½  inch long piece of vinyl plastic tubing (I.D. one—eighth inch;  inch) was slit lengthwise.  The stipe of the plant was placed  through the slit in the tubing with the holdfast extending from one end and the fronds of the plant, the other.  Using forceps, the holdfast—tubing  complex was pressed into the hole in the cement block until the top of the tubing was flush with the surface of the cement block (Figure 3).  This  technique proved to be satisfactory for about a 4 to 5 month period.  Plants  13 were lost after this time, apparently due to a hardening of the plastic tubing and the subsequent loss of the tubing’s inherent resiliency.  e)  Transplantation of Structurally Variable Plants Cement blocks (20.0 cm x 9.5 cm x 5.5 cm) were drilled with a  single hole in the center of the block.  A single plant was then  attached to each block in the previously described method. of plant complexity  Three levels  were used with each level differing in the number  of dichotomies per plant.  All plants were approximately 20 cm in height  and had either 30 or more dichotomies (high complexity), 20 dichotomies (medium complexity), or less than 10 dichotomies (low complexity).  Three  blocks of each complexity level were then transplanted to each of three intertidal sites in May, 1973.  The three sites were arbitrarily chosen  as being an area of either high Fucus density (cover value greater than 2 quadrat), medium Fucus density, or low Fucus density. 90% per 0.1 m Faunal colonization of the transplanted plants and the cement blocks was recorded over the experimental time period which extended to September, 1973.  Three control blocks with no plants attached were also placed in  each of the three sites.  f)  Fucus Density Effects Cement blocks (23.0 cm x 15.0 cm x 8.0 cm) were drilled with  20, 15, 10 or 5 holes with all holes clumped in the center of the block. Fucus plants of approximately the same height and with the same number of dichotomies were obtained in the manner described previously and attached one per hole to the experimental blocks.  Three of each type  14  of block—plant complex were placed in each of two areas, a high density Fucus area and a low density Fucus area.  The transplanted plants were  examined periodically for the presence of invertebrates over a period of ten weeks.  g)  Littorinid and Limpet Growth Experiments  An attempt was made to determine the effects of structurally different Fucus plants on the growth of two intertidal invertebrates commonly associated with Fucus;  Ljttorina sitkana and Acmaea pelta.  Stainless steel framed cages (15.0 cm x 10.0 cm x 10.0 cm) were enclosed in a nylon mesh bag (mesh diameter 3.0 mm) and attached to 23.0 cm x 15.0 cm x 8.0 cm cement blocks with stainless steel anchor bolts (Figure 4).  Provision was made for attachment of a single plant per cage.  The  experimental design consisted of cages containing either no Fucus, a plant trimmed to less than 10 dichotomies, or a plant with greater than 25 dichotomies.  Three cages of each design containing 10 Littorina  sitkana were placed in each of three intertidal areas: a low, medium, and high density Fucus area.  Prior to being placed in the cages each animal  was marked with orange cellulose base paint and the height of each animal determined with vernier calipers.  In a different set of cages 7 Acmaea pelta each were placed. Each cage contained either no Fucus, a plant trimmed to less than 10 dichotomies or a plant with greater than 25 dichotomies.  The length and  height of each animal was measured with vernier calipers prior to being placed in the cages.  Three cages of each experimental design were then  placed in each of a low, medium, and high density Fucus zone along with  15 the littorinid cages.  After a period of 18 weeks all animals were  removed from the cages and measured.  The possible loss of cages from log  damage at this time made it unfeasible to continue the experiment.  h)  Fucus Growth Measurements  To gain some insight into growth rates of mature and juvenile fucoids, experimental manipulative techniques were employed along with in situ tagging of specific plants.  Fifteen plants greater than 10 cm in  height were attached singly to cement bricks (23.0 cm x 15.0 cm x 8.0 cm) and placed in each of three zones;  a high intertidal zone corresponding  with the upper limits of Fucus, a mid intertidal zone corresponding to the area of maximum numbers of Fucus plants, and a low intertidal zone which was below the lower limits of any naturally occurring large fucoids. Growth and dichotomization of these plants was measured over time.  Five juvenile plants were selected from each of the above three intertidal sites and left intact on their natural substrate.  These  plants were tagged with orange colored surveying tape tied loosely above the holdfast and their position mapped to aid in their subsequent location. The growth of the plants was recorded over time.  h)  Investigations of Factors Affecting the Lower Intertidal Limits of Fucus  (I)  Pisaster—mediated mortality  An hypothesis was formulated to determine the effect of Pisaster ochraceus predation on Balanus glandulain the lower intertidal zone as a factor which acts to indirectly control the lower intertidal  16  distribution of Fucus.  To test this hypothesis, 10 large rocks  containing Fucus which was attached to Balanus glandula growing on the rocks, were transplanted into an area of high Pisaster activity. Similarly, 10 equally sized rocks containing Fucus which was attached directly to the rock surface were transplanted to the Pisaster area. All rocks were regularly monitored for the removal of Fucus.  A second test of the Pisaster—induced mortality hypothesis consisted of placing 6 rocks with 103 Fucus plants attached to Balanus glandula and 4 rocks with 70 Fucus plants attached directly to the rock surface into a large plastic meshed bag (vexar, mesh size 3.5 mm) along with 5 Pisaster.  The bag was sewn shut with nylon cord and placed  in the intertidal zone in the area of Pisaster activity.  The number of  fucoids remaining on the rocks was determined after 4 weeks.  (II)  Hermit Crab Grazing  During the course of this investigation field observations led to a hypothesis of hermit crab grazing causing heavy mortality of juvenile Fucus growing low in the intertidal zone.  To test this hypothesis rocks  containing 71 small fucoids were placed in the low intertidal zone along with rocks containing 25 juvenile plants which were enclosed in vexar bags. The numbers of plants and the condition of the plants remaining at the end of the experiment in August, 1973 was recorded.  Also two rocks with Fucus  were enclosed in a vexar bag and placed with two non—enclosed rocks in each of two small tidepools where there was an abundance of hermit crabs and an absence of fucoids. of grazing.  The rocks were checked periodically for signs  17 (III)  Balanus—Fucus Competition  Possible competitive interactions between Balanus glandula and juvenile Fucus were examined by the removal of any B. glandula which touched a selected group of 15 Fucus holdfasts.  A control group of 15  plants was left with surrounding B. glandula intact.  Both sets of plants  were mapped and their survival watched over time.  j)  Lighthouse Park Sampling Techniques  Sampling techniques used at Lighthouse Park were identical to those used at Bowen Island.  An attempt to duplicate the Fucus transplant  experiments of Bowen Island failed at Lighthouse Park because of the high wave—induced mortality of the transplanted plants.  As a result  experimentation at Lighthouse Park was limited to the examination of specific faunal—Fucus interrelationships.  k)  Mytilus edulis—Fucus Competition  Observations of dense accumulations of the mussel Mytilus edulis adjacent the lower edge of the Fucus zone resulted in an experiment to test the possible effects of M. edulis on the growth and survival of Fucus. Dense accumulations of Mytilus which grew around the base of and directly attached to juvenile Fucus plants were removed from 4 groups of six plants which were subsequently kept free of Mytilus with each visit to the experimental site.  Similar numbers of control plants were left with  their Mytilus complement intact.  The growth and survival of control and  cleared plants was recorded for the duration of the study.  In a similar experiment, all Mytilus were removed from 10  18 mature (greater than 15 cm in height) plants while a control group of 10 plants was left with their associated Mytilus intact.  Growth and  survival of these plants was also monitored for approximately 2.5 months.  1)  Limpet Marking Experiments  Repeated qualitative examinations of Fucus—inhabited zones at Lighthouse Park led to observations of many limpets, primarily Acmaea pelta, being found under the fronds of Fucus.  Such observations led to  an experiment to determine if this association was merely coincidental or, rather, if the limpets were choosing under—Fucus habitats. experiment commenced in May, 1973.  The first  Two adjacent areas, each about 2 m , 2  were chosen each of which contained a dense cover of Fucus and many A. pelta.  All the Fucus was removed from one of these areas and left  intact in the other.  The liiupets in the cleared area (n43) were marked  with red paint and all limpets in the intact area (n=60) were marked with orange paint.  The two areas were checked periodically for the presence  of marked limpets.  The experiment was duplicated a second and third time  with some slight modifications.  Two smaller adjacent areas each  approximately 0.25 m 2 were demarcated, one cleared of all Fucus, the other left in its natural state.  Twenty liinpets from a nearby site were obtained  and marked, 10 red and 10 orange.  Ten limpets were placed in the cleared  area and 10 in the uncleared area.  Each limpet was wetted with seawater  and observed until it was firmly attached to the substrate.  Each area was  checked for marked limpets with each trip to the experimental site.  19  m)  Laboratory Experiments  Laboratory experiments commenced in the summer of 1973 in a seawater equipped lab at the Vancouver Public Aquarium.  The  experiments were designed to duplicate some of the field experiments and to investigate specific interactions between certain invertebrates and Fucus.  (I)  Littorina and Acmaea Behavior Experiments  The ability of Littorina sitkana, L. scutulata and Acmaea pelta to detect the presence of Fucus and react to its presence was tested using the apparatus shown in Figure 5.  The apparatus consisted of a  plexiglass flow tray with two separate holding compartments, one of which held some Fucus and the other left empty.  Seawater flowed into each  compartment and over the bottom of the tray where the experimental animals were situated.  A 10 cm long plexiglass plate served to separate the two  streams of discharged water.  Carmine particles were used initially to  ensure that stratification of the two streams did occur on the bottom of the tray.  A drain hole was situated at each end of the tray through which  the discharged water flowed.  Fifty L. sitkana or L. scutulata were placed  in the center of the tray and the entire complex was covered with black plastic sheeting to remove any source of light which could influence the animal’s behavior.  The animals were left for 24 hours after which time  their position in the apparatus was noted. using a complement of 10 Acmaea pelta.  The experiment was repeated  20  (Ir)  Idothea Selection Experiments  This experiment was designed to determine if certain motile species which were found with Fucus, visually selected plants of a specific structural morphology.  The isopod, Idothea wosnesenski, and  amphipod, 1-lyale plumulosa, were selected for the experiment but problems in working with the small amphipods led to my using only Idothea. Four levels of plant complexity were selected for use in the experiment as follows: Level 1  Plants with more than 40 dichotomies  Level 2  Plants with 20 dichotomies  Level 3  Plants with 10 dichotomies  Level 4  Plants with 0—5 dichotomies  One plant of each level was anchored in the corner of a 10 gallon aquarium tank so that the blades floated freely in the water column.  In  the first series of experiments, 10 Idothea were placed in a small, open, weighted beaker in the center of the tank and left for 18—24 hours during which time the animals were free to migrate about the tank.  The sides of  the tank were blacked out to allow only surface light to enter the tank. After the time period each plant was removed and the number of Idothea found on each plant recorded.  The experiment was repeated with the  arrangement of the plants in the tank changed with each new experimental trial.  Complements of 15 and 25 Idothea were used in subsequent  experiments.  (III)  Pagurus Grazing Experiment  This experiment was designed to determine it hermit cz’abs  21  utilized Fucus as a food source as suggested from field observations. Twenty hermit crabs collected from Bowen Island were placed in a 10 gallon tank with a rock containing 30 small fucoids and a rock with 45 fucoids enclosed in a vexar bag.  Food material in the form of crushed  Mytilus and Balanus was added periodically to the tank in an attempt to duplicate the “normal” conditions under which the hermit crab is naturally found.  The plants were examined daily for signs of grazing  and the behavior of the crabs was observed during the course of the experiment.  Pisaster—Fucus Interactions  (IV)  This experiment was also a duplication of a similar field experiment.  Rocks containing 54 Fucus attached to Balanus glandula were  placed in a 15 gallon tank along with rocks containing 50 plants which were attached directly to the rock surface. were added to the tank.  Four Pisaster ochraceus  The survival of all plants and the behavior of  the starfish was recorded over time.  (v)  Detachment of Fucus by Mytilus  An observation of adult plants growing in clumps of Mytilus with their holdfasts detached from the substrate led to a laboratory experiment to determine if M. edulis was responsible for removing the plants from their substrate.  A rock with 70 fucoids of various heights  was enclosed with 200 Mytilus in a vexar bag and left in a 10 gallon aquarium tank for 2 months.  After this time the Mytilus were carefully  removed from the rock and the number of plants which remained firmly attached to the substrate noted.  22  RESULTS  a)  Bowen Island and Lighthouse Park Fucus Population Characteristics During the course of this study over 5,000 plants from the two  study areas were measured for total length and degree of dichotomization. The number of dichotomies per plant and the total height of plants differed between the two sites.  The comparisons were based on 100 plants  each, chosen randomly from each site.  At Bowen Island, 51% of the plants  were 0—3 cm high, 24% between 3—6 cm high and 11% between 6—9 cm high. The remaining 14% were between 9—18 cm hEgh (Figure 6—A).  At Lighthouse  Park 18% of the plants were between 0—3 cm, 18% between 3—6 cm, 21% between 6—9 cm, 16% between 9—12 cm, 18% between 12—15 cm, 6% between 15—18 cm, and 3% were greater than 18 cm (Figure 6—B).  The individual  plants at Lighthouse Park tended to be taller than those of Bowen Island. The degree of dichotomization also differed between the two areas. Plants at Lighthouse Park tended to have more dichotomies than those at Bowen Island (Figure 7).  Of the 100 randomly selected plants 83% of those  from Bowen Island had between 0—5 dichotomies, while only 54% of the plants from Lighthouse Park had between 0—5 dichotomies. The relationship between plant height and the. respective number of dichotomies for each area is displayed as regressions in Figure 8. Comparisons of the regression lines indicates that the degree of dichotomization is greater at Lighthouse Park.  Other plant character  istics compared between the two study areas were the number of plants per quadrat, the mean height of plants per quadrat, and the number of dichotomies per plant.  Table 1 shows the analysis of variance results of  23 these comparisons.  No significant difference in number of plants per  quadrat or the number of dichotomies per plant was revealed but the mean height of plants at Lighthouse Park was significantly greater than at Bowen Island.  Periods when plants were reproductive varied within the study areas.  On Bowen Island an upper intertidal form (Figure 9—A) attained  maximum development of conceptacles in winter and continued through early summer.  A lower intertidal form began to mature reproductively in June  and was apparent in a reproductive state through October (Figure 9—B). Recruitment of Fucus could potentially occur the year round on Bowen Island.  At Lighthouse Park, reproductive maturity as indicated by fully  developed conceptacles was maximal in the spring and summer months.  b)  Bowen Island Sampling  Vertical intertidal transects on Bowen Island revealed spatial and temporal patterns in the abundance and diversity of organisms associated with Fucus.  A variety of organisms occur associated with the  alga in one of the following fashions: Degree of Association  Example  1)  Directly attached  Balanus glandula, Mytilus edulis  2)  Slow moving, clinging forms  Acmaea pelta, Littorina sitkana  3)  Active clinging forms  Idothea wosnesenski  4)  Forms associated with algal exudate or water entrained by the plant  Hyale plumulosa  5)  Migrant forms which enter Fucus habitats at high tide  Cottid fishes  24 The total complement of species found in association with Fucus throughout the study period is illustrated in Table 2.  A  diagrammatic representation of some of the dominant invertebrates comprising the Fucus fauna is shown in Figure 10.  Seasonal trends in  the abundance of the dominant organisms, Littorina sitkana, L. scutulata, Mytilus edulis, and Hyale plumulosa are illustrated graphically in Figures 11 to 14.  The amphipod, Hyale plumulosa, displayed the greatest  variation in numbers on seasonal basis.  Very low numbers (less than 10  per 0.1 m 2 quadrat) could be found in the spring of 1973 and winter of l97344 while maximum numbers were found in the summer months of both 1973 and 1974.  The numbers of Littorina sitkana also demonstrated clear  seasonal fluctuations with a minimum number present in January, 1974, and peaks in population abundance during the spring and summer of 1973 and 1974. Little seasonal variation was evident in the numbers of Littorina scutulata and Mytilus edulis except for a decrease in abundance during winter. The numbers of L. scutulata were seldom greater than 20 per 0.1 m 2 quadrat (Figure 12—A) and the numbers of N. edulis were usually below 25 per quadrat (Figure 13—A).  Seasonal variation in species diversity of the assemblage of organisms associated with Fucus was evident.  Figure 15 illustrateS the  seasonal variability in species diversity (H’).  Peaks in mean (H’)  appeared in May 1973, August 1973, and July—August 1974.  Periods of low  diversity occurred in July 1973 and a decline in diversity was evident in the winter months of 1973—74.  Stepwise multiple regression analysis (UBC BND:02R) was employed to compare the variation in species diversity (H’), diversity per  25 individual (H), and numbers of organisms found on Fucus with the independent variables listed on page 11.  When all the seasonal data  are pooled, no definite trend emerges from the analysis (Table 3). For species diversity (H’) the total number of dichotomies accounted for 16.41% of the variation in (H’) with the intertidal quadrat position accounting for 5.80% of the variation and the mean height of plants, 3.36% of the variation.  For diversity per individual, (H), the number  of dichotomies accounted for 21.02% of the variation with distance along the intertidal transect and the mean height of plants accounting for 6.38% and 3.93% of the variation respectively. height of all plants pert  The total cumulative  quadrat was responsible for a 4.24% reduction  of the variation in numbers of organisms with the number of plants accounting for 3.71% and quadrat position along the intertidal transect 1.76%.  The seasonal variation in mean numbers of organisms per quadrat  is illustrated in Figure 16.  Separating the data into respective seasonal  categories yielded results which indicate that different factors are attributable for most of the variability in species diversity and numbers of organisms found associated with Fucus at different times of the year (Table 4).  In January, 1974, Fucus height diversity accounted for the  greatest reduction in species diversity (H’).  The position of the quadrat  along the intertidal transect was responsible for 31.40% of the variation in (H’) during April—May and 14.06% of the variation in August.  In July  and in the September—October time period reduction of the variation in (H’) was closely associated with plant structural characteristics such as mean number of dichotomies (July) and mean plant height (September—October).  The seasonal variation in Fucus height diversity is shown in  26 Figure 15 along with the variation in species diversity (H’). Synchronous fluctuations are apparent between the two indices with the closest correlations between (H’) and Fucus height diversity occurring when both values are at their seasonal minimum (July, 1973; 1974).  January,  Regression analysis comparing the relationship between Fucus  height diversity and species diversity resulted in a significant correlation between the two variables (Figure 17).  The distributions of the dominant organisms on individual plants are shown as frequency distributions of numbers of organisms against distance along the plant from the plant holdfast.  The numbers  of Littorina sitkana on plants of five size ranges (0—5 cm, 5—10 cm, 10—15 cm, 15—20 cm, and greater than 20 cm) are shown in Figure 18.  As  the size range of the plants increases, the distribution of L. sitkana on the plants shifts with peaks in abundance shifting from a position on the lower 0—1 cm of the plant (adjacent to the holdfast) for plants 5 cm or less, to a peak over 20 cm from the holdfast on plants greater than 20 cm in height.  The amphipod distribution, Figure 19, does not follow  any specific pattern.  On shorter plants the amphipods tend to be clumped  near the holdfast while on taller plants no clear pattern of amphipod distribution is evident.  The distribution of Mytilus edulis is skewed  for plants 0—10 cm in height with the distribution becoming more dispersed on plants greater than 10 cm (Figure 20).  The species diversity of the organisms on the substrate within the quadrats showed little seasonal variation relative to the diversity of the fauna associated with Fucus except for a peak in May, 1973.  A  list of those organisms found on the substrate under the Fucus canopy is  27 shown in Table 2.  Multiple regression analysis indicated that Fucus  height diversity accounted for most of the variation in substrate species diversity (H’) and diversity per individual (H) which was only 6.98% and 6.80% respectively.  The total cumulative height of the plants per  quadrat accounted for 9.82% of the variability in numbers of organisms per quadrat.  Figure 21 displays the change in mean substrate diversity  (H’) over time.  c)  Fucus Transplantation Results  Over the 12 week period during which active colonization of the transplanted Fucus plants occurred the species diversity of the colonizing community varied considerably.  Figure 22—A shows the weekly  variation in mean species diversity (H’) for the three plant complexity types transplanted into a low Fucus density area.  Variations in diversity  with each plant type were quite synchronous except for the diversity on medium complex plants which peaked after five weeks to a level far greater than that of the other two plant types.  A drastic decline followed this  peak with diversity levels again becoming synchronous with the other plant levels.  Plants of the lowest level of complexity were the last to  be colonized (3 weeks) and were virtually free of organisms following the the 12 week experimental period.  The plants of the highest level of  complexity generally maintained a more diverse community of organisms. The dominant organisms for the transplanted plants were Littorina sitkana, L. scutulata, Hyale plumulosa, Mytilus edulis, and Idothea wQsnesenski with littorinids being the first species to be found on the transplanted plants.  28 Those plants transplanted into a zone of medium Fucus density also exhibited fluctuations in species diversity (H’) (Figure 22—B).  Colonization of these plants was somewhat slower than  of the plants in the low density Fucus area.  No clear trends emerged  except for a peak in diversity around the eighth week followed by a decline on the low and high complexity plants with an increase in diversity to the twelfth week.  For those plants of the high density zone, synchronous fluctuations were again evident with increases and decreases in diversity over time.  Colonization occurred after one week on the low and high  level of complexity plants, but significant colonization of medium complex plants did not occur until between the fifth and eighth week (Figure 22—C).  Figure 22—D shows all three categories of plants combined  over all three density areas. the highest complexity plants.  The greatest fluctuations are evident on After eight weeks species diversity (H’)  was maximum for the high and medium complexity plants unlike the low level plants which tended to increase in a series of steps up to the twelfth week.  d)  Density Transplants  The results of investigations of the effect of plant density on the diversity of the colonizing population were hampered somewhat by heavy losses of the transplanted plants.  The experiment had to be  concluded after 10 weeks because of these losses.  Figure 23—A shows the  change in mean species diversity (H’) over time in the low density Fucus area.  For those blocks containing 0—10 plants, species diversity was  maintained at a low level (less than 0.75) throughout the experimental  29 period.  For blocks with more than 10 plants, plant losses halted  analysis after the second sampling period.  In the zone of high density  Fucus, mean (H’) was generally higher (greater than 1.15) than values obtained in the low density Fucus zone (Figure 23—B).  Diversity of the  assemblage of organisms on Fucus peaked after five weeks for both high and low density blocks.  The high density blocks maintained a slightly  more diverse, although not significantly greater, community than low density blocks.  It is interesting to note that the time of the peak  diversity (5 weeks) coincides with the time of maximum species diversity obtained in the intertidal sampling program, e.g., August, 1973. Figure 23—C displays the mean (H’) over time for both the high and low density areas combined.  The initial colonizers in both high and low density Fucus areas were Littorina sitkana and L. scutulata.  The numbers of L. sitkana and  L. scutulata increased over about a five week period when substantial numbers of the amphipod, Hyale plumulosa were noticed.  Idothea was present  after 5 weeks and Mytilus began to attach to overhanging fronds after about 8 weeks.  At the end of the 10 weeks, L. sitkana and L. scutulata  again numerically dominated the Fucus faunal community and the numbers of Hyale and Idothea had declined.  Figure 24 shows the change in mean numbers  of organisms over time for both high and low density Fucus areas.  For both  areas the mean numbers of organisms found on low density blocks were similar and at no time were more than 50 individual organisms present. both areas the numbers of organisms declined towards the end of the experiment.  Results for the high density blocks are unfortunately  incomplete yet they illustrate a trend of a rapid increase in organisms  In  30 to a maximum number of 146 in the low density Fucus area and 192 in the high density Fucus area followed by a marked decline in both areas. e)  Littorina and Acmaea Growth Experiments  Significant differences in limpet growth rates between the three treatments (no Fucus, medium complexity Fucus, and high complexity Fucus) were not evident.  The loss of paint marks on some individual  animals and the mortality suffered by others rendered impossible valid statistical comparisons.  Length—height regressions of the initial and  final animal sizes for each treatment are presented, however, for illustrative purposes (Figure 25).  Growth rates of Littorina sitkana were similar for all treatments.  Analysis of variance comparisons (Table 5) of the final  sizes of the animals for each treatment resulted in an insignificant F—value (F=0.232, p=O.O5).  f)  Factors Affecting the Lower Intertidal Limits of Fucus  Subjective observations of the intertidal region reveal a zone of Fucus with very distinct lower intertidal boundaries (Figure 26). The distinctive nature of the distribution of mature plants coupled with observations of juvenile plants and clumps of mature plants growing below this marked boundary suggested that a biological rather than a physical influence was determining the lower distributional limits of Fucus.  The  presence of Pisaster ochraceus located up to the lower level of Fucus and the obvious destruction of Balanus glandula and Mytilus edulis through Pisaster predation below the Fucus zone indicated that the predatory action  31 of ?isaster in the low intertidal zone was indirectly causing heavy mortality of Fucus by destroying the barnacles to which the fucoids were attached.  The placement of rocks containing Fucus plants which were  attached to Balanus glandüla proved to be an unsuccessful test of the Pisaster—induced mortality hypothesis.  This, I believe, is the result  of the seasonal migration patterns illicited by Pisaster.  In May, when  the experiment was initiated, Pisaster was evident in the mid—intertidal region.  However, Pisaster rapidly disappeared from this area by mid May  presumably from migration and not predation, and were not evident until late August, 1973.  Diving observations during the summer revealed large  aggregatipns of Pisaster in the subtidal zone.  The second test of the hypothesis was successful.  Of the 103  plants attached to Balanus glandula on rocks placed in the vexar bag only 31 remained after 4 weeks representing a mortality of 62.1%.  Of an  original total of 70 plants attached directly to the rock surface, 64 remained after 4 weeks with a mortality of only 9.3%.  Those plants which  were originally attached to barnacles were found in the bag, their holdfasts still attached to a barnacle plate.  Those plants remaining on  the rocks were attached to intact barnacles that had not been eaten by Pisaster or were directly attached, to the rock surface.  This experiment  was duplicated under laboratory conditions where similar results were obtained (discussed later).  g)  Hermit Crab Grazing  Definite signs of what appeared to be hervivore grazing on plants in the lower intertidal zone was noticed in early August, 1973.  32  Prior to this time no visible indication of grazing was noticed on juvenile plants growing in the low intertidal zone.  Typically, grazed  plants differed from ungrazed plants in having serrated edges (Figure 27). Of 71 juvenile fucoids (less than 3.0 cm in height) transplanted to the low intertidal zone at the beginning of August, 1973, a total of 30 remained on August 26, representing a mortality of 43.3%. surviving plants were extensively grazed.  All the  The 25 plants which were  enclosed in a vexar cage were all present after the above time period with no visible signs of grazing.  Similar results were obtained with  caged and. uncaged plants which were placed in tidepools.  Hermit crabs could often be found situated on the tips of the plants in tidepools engaged in what appeared to be grazing activity. Groups of plants placed in the low intertidal zone in June, 1974 remained structurally intact until August when grazing by Pagurus began again.  h)  Balanus-Fucus Competition  The examination of possible competitive interactions between Balanus glandula and Fucus yielded no definite conclusions.  The mortality  of all plants, treatment and control, was too high for valid comparisons between the two groups of plants.  No significant reduction in Fucus  mortality occurred as a result of removing those barnacles which encroached upon Fucus holdfasts.  i)  Plant Growth Studies  Growth studies of tagged plants from the high and mid inter tidal areas are displayed in Figure 28.  The mean height of plants at the  start of the experiment (June, 1973) in the upper intertidal zone was  33 2.62 cm.  At the conclusion of the growth period in October the mean  height was 7.47 cm representing a total mean growth rate of 4.84 cm over a five month period.  The mean height of plants in the mid—intertidal zone at the initiation of the experiment was 2.05 cm with a final mean height of 8.67 cm representing a growth rate of 6.62 cm over the 5 month growth period.  These rates indicate a trend of more favorable growth in the  mid—intertidal areas.  Juvenile plants were also tagged in the low intertidal zone for measurement of growth rates but mortality of these plants was too high to allow for meaningful comparisons with other tidal levels.  In January, 1974 a new settlement of Fucus appeared on some of the cement blocks that had been left over winter.  The mean height of  10 randomly selected plants at this time was 0.029 cm.  The density of  plants on the blocks averaged 173 plants/lOO cm 2 (mean of 5 quadrats). The growth rates and increase in dichotomization were followed until September, 1974, and are depicted in Figure 29.  The rate of growth  was rapid, growing a mean of 14.8 cm from January to September. Dichotomies greater than 1 cm in length did not appear until June when the plants were approximately 7—8 cm in height.  After this time dichot  omization increased from a mean of 4.8 to 28.2 in September.  The density  of plants declined considerably over the 9 month study period, with the final mean density in September only 27 plants /100 cm . 2  The actual  mechanisms of the thinning process are unknown although it seems probable that Idothea predation resulted in the death of many plants.  In  April, 1974, a population of isopods (Idothea wosnesenski) colonized the  34 Fucus plants on the cement blocks and persisted until September. Grazing marks from Idothea (Figure 30) and Pagurus on smaller plants The grazing marks left by Idothea differ from those  were quite evident.  of Pagurus in being much larger and lack the serrations incurred on the plant by Pagurus.  An assemblage of L. sitkana, L. scutulata, Hyale plumulosa  and occasionally Pagurus became associated with the plants over the sampling period.  The mortality of large transplanted plants was high, especially for those plants transplanted into, the low intertidal zone. Analysis of variance comparing growth rates after three months indicated no significant differences in growth rates between the three areas (Table 6).  Extensive grazing and loss of fronds from the low intertidal  plants prevented comparisons of rates of dichotomization between the three areas.  j)  Lighthouse Park Sampling  The faunal community associated with Fucus at Lighthouse Park was less diverse than the Bowen Island fauna.  A single species,  Mytilus edulis, tended to dominate the community and often, as is discussed later, played an important role in controlling the intertidal distribution of Fucus and, perhaps, the morphology of the plants. Acmaea pelta, Littorina scutulata and L. sitkana comprised the remaining numerically dominant forms but these species, relative to Bowen Island, were few in numbers.  Figure 31 shows the seasonal fluctuations in mean  species ciiversity (H’) with an initial low in early May, 1973, (H’=0.l73) followed by seasonal maximum (H’=l.043) in mid May with a secondary low of  35 0.529 in July, 1973.  From August to April, 1974 no dramatic increase  or decrease in diversity was apparent although sampling was not carried out during the winter months because of the difficulty involved with working in the area at night.  A plot of seasonal changes in mean numbers  of individuals reveals fluctuations with the peaks in abundance being in May and August, 1973 (Figure 16).  Table 2 gives a species list of those  organisms found associated with Fucus at Lighthouse Park. numbers of dominant organisms are shown in Figure 11—14.  Changes in the Levels of  Littorina sitkana and L. scutulata abundance were characteristically low except for a peak of 15 L. scutulatain mid May, 1973.  High levels of  Mytilus edulis were found throughout the sampling period with the maximum number obtained per quadrat being 800 early in May, 1973.  Aiuphipods,  Hyale plumulosa, were seldom found except during the summer months when they peaked in abundance.  Fucus height diversity fluctuations are  illustrated along with species diversity (H’) in Figure 31.  As with the  Bowen Island comparison, the fluctuations in mean Fucus height diversity are quite synchronous with mean species diversity (H’) on a seasonal basis. Regression analysis of the pooled seasonal values revealed no significant correlation between Fucus height diversity and species diversity (H’). Multiple regression analysis (UBC BND:02R) was incorporated to determine which independent variables were most important in affecting species diversity and the total numbers of organisms (Table 3).  The dependent  variables (H’), (H), and numbers of organisms were transformed logarithmically (base 10) to reduce variations from northality.  No clear trends  emerged from this analysis when all the seasonal data are pooled.  The  independent variable, number of dichotomies perunit length of Fucus, was most important, accounting for 10.25% of the variation in (H’) and 10.12%  36 of the variation in (H).  The dry weight of Fucus was associated with  a reduction of 5.15% and 4.54% of the variation in (H’) and (H) respectively.  The number of dichotomies per plant contributed to most  of the variation in numbers of organisms, 13.79%, with 10.97% being accounted for by the number of dichotomies per unit length of Fucus. Seasonal separation of the data into Spring, Summer, and Autumn components and subsequent application of multiple regression analysis led to the results summarized in Table 7. diversity is shown in Figure 21.  The change in mean substrate  Multiple regression analysis of the  substrate diversity and number of organisms yielded no highly correlated associations.  Meaningful results could not be obtained from recordings of positions of organisms on individual plants because of the often sparse fauna and the tendency of Mytilus edulis to dominate on the plants.  The  distribution of Mytilus is shown for plants 0—10 cm in height and plants greater than 10 cm in height (Figure 32).  Approximately 92% of the  Mytilus were attached to the lower portion of the stipe (0—3 cm from the holdfast) on plants ranging in size from 0—10 cm.  The Myilus  distribution on plants greater than 10 cm is more variable than on plants less than 10 cm in height with the maximum numbers again occurring near the holdfast but with a secondary maximum occurring at 5 cm. k)  Mytilus—Fucus Competition (Juvenile Plants) The detrimental effect of M. edulison the growth of juvenile  Fucus plants was established through Mytilusremoval experiments.  For  one replicate experiment, the growth rate of those plants cleared of  37 M. edulis was similar to those plants with Mytilus left intact for approximately 23 days (Figure 33—B).  After this time however, Mytilus  overgrew the plants that were not cleared of Mytilus and subsequent growth of these plants was not evident.  The plants removed from the  influence of Mytilus grew a further 3.08 cm (mean of 6 plants) in 71 days. Similar results were obtained with a second group of six plants where no further increase in growth of those plants with Mytilus was evident after 48 days (Figure 33—A).  The mean increase in growth of plants  cleared of Mytilus after the 48 days was 8.35 cm.  1)  Mytilus—Fucus Competition (Adult Plants)  The growth and survival of larger plants was also improved in the absence of Mytilus.  Growth rates of plants cleared of Mytilus could not be  compared with plants influenced by Mytilus because after approximately three weeks, all plants with attached Mytilus had become “fused” to the rock substrate and the surrounding Mytilus bed.  Characteristically, a few  Mytilus individuals on the plants would attach via their bysall threads to other mussels on the rock surface.  Other mussels would then attach along  the length of the plant and eventually cover the entire plant leading to the eventual death of the plant.  Plants cleared of Mytilus did not suffer  this fate, but rather, they continued to grow and develop.  The plants  cleared of Mytilus grew a mean height of 8.17 cm in 2.5 months.  A secondary effect of Mytilus on Fucus was noticed where occasionally large Fucus plants could be seen extending from extensive Mytilus clumps.  Examination of some of these plants revealed that their  holdfasts were clear of the substrate and the plants were being supported  38 by attachment of the mussels.  Presumably, the pressure exerted by  the mussel bysall threads under the influence of wave force, forced the holdfast from the substrate.  This hypothesis was tested in the  laboratory and is discussed later.  m)  Limpet Marking Experiment  Limpet migration out of areas cleared of Fucus was significantly greater than from areas of intact Fucus stands. results for 3 experimental trials are shown in Table 8.  The  In May, 1973,  32 of 60 marked limpets remained in the Fucus area after one week while only 8 of 43 original marked limpets remained in the cleared area.  Of  those marked limpets originally in the cleared area, 5 had migrated into the adjacent Fucus area.  A test comparing the proportions remaining in  each area (Ho: the proportion remaining in the cleared area in uncleared area) was carried out by calculating a 1973).  The c value (Table 8) is 4.0 at p  is rejected;  <  proportion  value (Woolf,  0.001 so the null hypothesis  the proportion of limpets remaining in the intact Fucus area  is significantly greater than that of the cleared area.  The experiment  was duplicated in June with smaller numbers of limpets and similar results were obtained.  After 27 days, 6 marked limpets of an original 10 remained  in the Fucus area along with 2 that had migrated in from the cleared area. Only one marked limpet of an original 10 remained in the cleared area. After two months 8 marked limpets could be found in the Fl4cus area with 4 of those having originated in the cleared area while no marked limpets remained in the cleared area.  The third duplication (Table 8, trial 3)  yielded similar results to the two previous trials.  39 n)  Laboratory Experimentation  (I)  Behavior Experiments  Laboratory behavior experiments dispelled a theory of three invertebrate species being able to chemotactically locate Fucus.  Neither  Littorina sitkana nor L. scutulata reacted positively to the presence of Fucus.  The littorinids dispersed towards the sides of the experimental  apparatus with no apparent tendency to distribute themselves on either side.  With a sample of 50 L. sitkana averaged over 10 replicate trials  the mean number of L. sitkana found on the Fucus side of the tank was 19.8 with 22.1 being found on the control side.  Analysis of variance showed  the mean numbers on each side did not differ significantly (Table 9). Similar findings were obtained using L. scutulata.  Of 7  replicate trials the mean number of L. scutulata found on the Fiicus side was 22.8 with 25.8 individuals being found on the control side.  Analysis  of variance again revealed that no significant difference between the numbers found on each side existed (Table 9).  Acmaea pelta did not migrate in significant numbers to either side of the tank but, rather, tended to remain clumped in the center of the tank or clumped to each other such that meaningful analyses of their resultant distributions could not be made.  (II)  Idothea Selection Experiments  The experiments with Idothea to determine if the animal preferentially selected algae of greater complexity suggests that Idothea does prefer plants with a greater degree of structural complexity.  The  40 four types of plants used were ranked from level 1 (most structurally complex) to level 4 (least structurally complex) in the experiments. Using 10 Idothea in the first experimental series, the animals aggregated on the most complex plants (level 1, Figure 34—A).  With 4  trials combined, 22 individuals were found on the level 1 plants, 6 on level 2, 6 on level 3, and none on level 4.  Similarly, using 15 Idothea per trial there was a noticeable tendency for the animals to distribute themselves on the most complex plants (Figure 34—B).  Of a total of 4 trials combined, 40 were found on  level 1, 9 on level 2, 1 on level 3 and none on level 4.  When 25 Idothea  were used per trial, similar distributions were found (Figure  34—c).  The cumulative total for 6 trials was 98 individuals on level 1, 19 individuals on level 2, 9 on level 3, and 2 animals on level 4.  Chi  square analysis indicates the significant tendency ofIdothea to select plants of the greatest complexity (Table 10).  (III)  Pagurus Grazing  Laboratory observations of Fucus in the presence of hermit crabs suggested that Pagurus can impose extensive grazing pressure on juvenile fucoids.  Following submersion in the presence of Pagurus, all the Fucus  plants displayed characteristic grazing marks similar to those found on plants apparently grazed by Pagurus in the field.  The edges of the fronds  appear serrated (Figure 27) when compared with ungrazed plants. plants were often completely grazed from the rock surface.  Smaller  Examination of  Pagurus fecal pellets revealed cells which resembled Ftcus cortex cells.  41 (IV)  Pisaster—Fucus Interactions  The field experiment designed to test the hypothesis of Pisaster—induced mortality of Fucus attached to Balanus glandula was duplicated in the laboratory with similar results.  After two weeks  50 of the 54 (92%) Fucus plants attached to Balanus were removed by Pisaster preying on the substrate barnacle.  None of the 50 Fucus plants  attached directly to the rock surface suffered any mortality.  The  experiment was replicated five times with the mortality of Fucu attached to Balanus being greater than 90% for each trial.  No mortality of those  Fucus plants attached directly to the rock surface was evident. (V)  Mytilus Removal of Fucus After a two month period 11 of the 70 plants (15%) had been  removed from the substrate presumably from pressure exerted by the mussels. All the plants removed were small (0—5 cm) with none of the larger plants being removed.  42 DISCUS S ION  a)  Diversity and Community Structure  Associated with intertidal populations of Fucus is a faunal community which varies in diversity both seasonally and spatially.  Some  of the animal genera found on Fucus are similar to those recorded in other studies, e.g., Idothea and Littorina, (Lewis, 1964); (Wieser, 1952;  Bousefield, 1957;  Lewis, 1964).  Hyal,  The diversity of the  fauna of the two study areas as expressed by (H’) differed with the faunal diversity on Bowen Island being generally greater than at Lighthouse Park although the types of organisms found in both areas were similar.  The relative contribution of fluctuating populations of  animals such as amphipods on Bowen Island was to increase faunal diversity during times of population peaks.  The lack of distinct  fluctuating populations of organisms at Lighthouse Park tended to reduce overall diversity.  Seasonal fluctuations of the fauna associated with Fucus have been noted by other researchers (Haage and Jansson, 1970;  Hagerman, 1966).  Generally, in these studies lowest numbers of organisms were found in the winter months and maximum numbers in the summer months.  The causal  factors operating behind the fluctuations are probably those which affect all intertidal populations, i.e., high winter mortality and maximum recruitment of the populations in spring and summer.  The use of Fucus  in the summer months as a refuge from environmental stresses, such as high temperatures, may contribute to the increased numbers of certain organisms found associated with the alga in this season.  Fucus tends to  43 trap water among its fronds and this action, coupled with natural exudation maintains a humid, relatively cool environment.  Periodic  measurements of temperature taken with a thermometer placed among the fronds of Fucus showed temperatures of up to 5°C below air temperature. The environment found among Fucus fronds during summer is probably a favored environment for certain organisms such as amphipods. When the diversity values over thá total sampling period for Bowen Island are pooled, multiple regression analysis suggests a relationship between the number of plant blade dichotomies per quadrat and animal species (H?) and diversity per individual (H). of correlation however (R 2  =  16.41 (H’) and R 2  of tremendous temporal and spatial variation.  =  The low degree  21.02 (H)), is the result  This relationship is  similar to the trend noted in terrestrial communities of increasing insect species diversity with increasing plant structure (Nurdoch, Evans, and Peterson, 1972).  An increase in the degree of dichotomization of a plant  results in an increase in the 3—dimensional structure of the plant.  Such  an increase in structural complexity may act to separate populations of potentially competitive species.  The numbers of individual organisms,  unlike species diversity, is more closely associated with the total cumulative height of the plants per quadrat.  The total amount of physical  space in terms of total length may be more important than the amount of partitioning of that space through dichotomization with respect to the total numbers of organisms found.  The importance of the degree of dichotomization is also apparent at Lighthouse Park where the number of dichotomies per unit length accounted for most of the variation in (H’) and (H) with the  44 number of dichotomies per plant accounting for most of the variation in the total numbers of individual organisms.  Fucus height diversity  when averaged for each sampling period is synchronous with changes in mean animal species diversity (H’) which suggests the importance of structural complexity (e.g., MacArthur’s foliage height diversity, MacArthur, 1965) in contributing to species diversity.  The trends established with the pooled data are not apparent when one considers the seasonally partitioned data.  The lack of a clear  seasonal trend might imply that those factors governing or affecting community structure are not continual seasonally but vary over time. Thus at any specific time, no primary causal factor could be predicted as the one contributing most to the. resultant faunal species diversity.  The question of why species diversity on Bowen Island is higher than at Lighthouse Park remains unanswered and is open to speculation.  One reason may lie in the differences between the relative  mortality rates of populations of invertebrates in both areas.  Lighthouse  Park, relative to Bowen Island, could be considered an area of greater stress in terms of the amount of physical damage incurred on the biota through storms and drift logs.  Although not measured, damage to the  intertidal biota from drift logs at Lighthouse Park is probably considerable, a supposition supported by previous studies in the area (Ross and Goodman, 1974).  The action of these logs would be to physically remove large  numbers of organisms from their substrate.  Dayton (1971) considers log  damage a major contributing factor in the creation of “open spaces” in the intertidal zone.  45 One factor which may determine the types and numbers of organisms found associated with Fucus is the so—called whiplash effect (Lewis, 1964), whereby Fucus under the influence of wave pressure tends to dislodge or prevent barnacles and other organisms from settling on the substrate.  Presumably the whiplash effect would be greater in areas  of greater exposure and may tend to prevent the settlement or attachment of forms which might normally be present in less exposed areas.  Hence,  at Lighthouse Park there may be a physical interference phenomenon occurring which is not apparent at the less exposed Bowen Island site.  The decreased diversity at Lighthouse Park could also be due to greater recruitment and survival of Mytilus edulis, and the formation of a single species complex.  Harger and Tustin (1973a) suggest that two groups  of factors can influence the successional patterns in marine communities. The first is the availability of colonizing organisms and the second is the structure of the resident community.  The presence of a large  population of Mytilus may prevent establishment of further species through competitive exclusion which serves to maintain a simplified assemblage of organisms on Fucus.  The phenomenon of Mytilus becoming competitively  dominant in the intertidal zone is described by Paine (1966, 1974).  In  the absence of predators Mytilus californianus dominated the intertidal zone resulting in the elimination of up to 25 macroscopic invertebrate species.  The nature of the substrate to which Fucus is attached may also play a role in determining the types of animals found on the alga. Typically, Fucus is found growing on large rock masses in the intertidal zone in the study area at Lighthouse Park whereas on Bowen Island, Fucus  46 abounds on small boulders.  The fauna I found associated with Fucus is  not unique to the alga but rather, is commonly associated with under—rock and crevice habitats.  For example, the hermit crab Pagurus is commonly  found in crevices, tidepools, or under rocks.  On Bowen Island, Pagurus  could readily be found among Fucus which was growing on small rocks.  At  Lighthouse Park however, the only Pagurus found associated with Fucus were located in crevices or tidepools.  Similarly, Hyle and Idothea are  commonly found in an under—rock habitat.  Populations of fucoids growing  on cliffs and very large boulders do not have a large potential source of organisms which could emigrate from an under—rock habitat to aFucus habitat.  Peaks in the abundance of organisms associated with Fucus on  Bowen Island may be the result of dispersion from “natural” habitats due to inter— and intraspecific interactions in space or food—limitations.  The  subsequent decline in numbers associated with Fucus in winter months may be a function of decreased competitive interactions resulting from winter mortality which tends to decrease dispersal pressure from natural habitats to Fucus habitats.  Another consideration may be linked with the structure of the Fucus pse.  Substrate complexity or diversity, both on a macro— and  microscale has been considered to be an important attribute in determining the chain of successional events from initial colonization to a diverse community (Seed, 1969;  Bayne, 1965;  Harger and Tustin, 1973a).  Differences in the microtopography of the surface of Fucus frond may in turn result in different species associations or differences in the rates of colonization.  For example, Fucus at Bowen Island contained many  prominent caecostomata  which tended to increase the surface complexity of  47 the alga.  Also, the degree of exudation may contribute to the presence  or absence of certain forms such as Hyale.  Mytilus edulis larvae have  been shown to prefer filamentous surfaces on which to attach (Bayne, 1965).  Fucus at Lighthouse Park is often found with considerable amounts  of the epiphyte Elachisteafusicola, the filaments of which may serve as attachment sites for Mytilus larvae.  A final consideration of differences in diversity between the two study areas involves the palatability of Fucus in both areas. Recently, much effort has been directed towards substantiating the role of metabolic substances as chemical defense mechanisms against predation in higher plants (Levin, 1971;  Janzen, 1969).  Vadas (1968) suggests  that the benthic alga Agarum, has evolved a chemical defense system which acts to  “...  effectively reduce the incidence of grazing...”  The presence  of Idothea and signs of grazing at Lighthouse Park tends to disfavour this hypothesis for juvenile plants.  Many larger, mature plants however, are  never found with any associated organisms or visible signs of grazing even though many organisms can be found on nearby plants.  This suggests  possible age specific differences in the palatability or “attractiveness” of the plants to organisms.  Deriving relationships between measurable structural features of intertidal algae and associated faunal communities presents a major problem in terms of the high degree of variability which prevails between low and high tides.  At low tide the plants assume a static position  which comprises a specific volume of space.  At high tide the plant is  subject to wave and current forces such that the position maintained by any given plant varies considerably.  In light of these constraints in  48 defining the position and volume of space occupied by the plant it is difficult to apply the same measures of vegetation structural diversity as has been done with higher plants.  Of importance to the question of  which component of algal structure is most highly correlated with animal species diversity and community structure is the timing over a tidal cycle with which motile animals can establish themselves with a particular Fucus plant.  Diving observations over Fucus beds at high tide  revealed that motile species move freely among the Fucus fronds.  Hyale,  Idothea, Pagurus and Gnorimosphaerorna were often seen swimming about the plants.  Selection for specific plants or groups of plants by these  species would probably occur as the tide ebbed with the animals remaining affixed to the plants they selected throughout the low tide period.  Other  forms such as Littorina sitkana and L. scutulata become associated with the alga once the tide has fallen and they are able to disperse among the fronds. 1) 2)  Two forms of colonization then,are apparent.  These are:  selection by highly motile forms, e.g. Idothea ‘Passive’ selection by “erratic” dispersers, e.g. Littorina. Unlike investigations of terrestrial plant—animal associations  where active competition and resource partitioning is thought to lead to a division of the habitat and coexistence (MacArthur, 1958, 1965) competition among the forms on Fucus is minimized by environmental variability (high and low tides) and the role of Fucus as a refuge rather than a food source for most forms.  MacArthur (1965) summarizes  the theory of within habitat diversity stating that the number of species within a habitat can be expected to increase with habitat productivity, structural complexity, lack of seasonality of resources, the degree of specialization, and reduced family size.  An increase in structural  49 complexity of Fucus on Bowen Island would probably not result in an increase in species diversity.  In terms of the species pool available  on Bowen Island, those forms presently found on Fucus represent the species complement which is able to colonize the alga.  An increase in  the diversity of potential colonizers would be required to increase the diversity of the Fucus associated fauna.  The results from the individual Fucus transplant experiments suggest that the motile fauna associated with Fucus is highly transient. Rapid colonization of the individual plants was followed by fluctuations in mean diversity levels regardless of the density of the Fucus zone into which the plants were placed.  Thus a “climax” fauna is not established,  at least over the time period the process was observed.  The structure  of individual plants over the range of variation tested did not influence the diversity of the colonizing fauna which suggests that the structure of groups of plants is more likely to determine the nature of the assemblage of organisms found therein.  The diversity of the fauna which  colonized groups of plants differed between areas of low density Fucus and areas of high density Fucus but within each area the diversity measured over time was similar for groups of plants with more than 10 individuals per group and groups with fewer than 10 individuals.  The number of plants  required for maximum diversity to be attained on bricks 23.0 cm x 15.0 cm x 8.0 cm is less than 10 plants.  Areas of high density Fucus are  preferable to low density areas and may be selected by certain organisms. Idothea for example, was shown to clearly select plants of greater complexity in the confines of an aquarium tank.  On a larger, natural scale,  Idothea would probably select areas of dense Fücus because such areas would  50 represent optimal feeding sites and superior refugia.  The importance  of density was established from the density transplant experiments. Differences in diversity between areas of high and low density Fucus implies there is some selection by motile forms for areas of dense Fucus.  The results of lab experiments designed to test the ability of Littorina sitkana, L. scutulata, and Acmaea pelta to locate food sources agrees with results in other experiments.  Behrens (1971) concluded that  L. sitkana is not able to chemotactically locate food.  Although the  presence of Fucus did not influence the growth rate of Acmaea or Littorina, the limpet marking experiment indicates that Acmaea utilizes Fucus as a refuge, probably against heat stress and predators.  Southward  (1964) suggests that limpet growth is enhanced in a favorable and damp habitat such as that found under a Fucus canopy.  The distribution of the dominant organisms on individual Fu.gus plants is shown to vary with the height of the plant.  This variation is  probably a result of increased plant contact with the substrate provided by taller plants and is not the result of selection of specific portions of the plant by particular organisms.  The tendency of Mytilus to be  distributed near the holdfast in all size categories of plants except for the largest at Bowen Island may be the result of Mytilus crawling from the substrate up the stipe of the plant and attaching near the base of the plant.  On larger plants Mytilus probably attaches to the plant when the  fronds of the plants are lying prostrate over a population of mussels. At Lighthouse Park the distribution of Mytilus on Fucus tends to be clumped toward th base of the plants on all sized plants.  This could be  the result of the “whiplash” effect described earlier which would prevent  51 establishment of Mytilus on the outer extremities of the plant.  Access  to shorter plants by littorinids is gained by crawling up the stipe while access to taller plants is obtained by moving onto the fronds when the plant is lying flat on the substrate.  b)  Lower Intertidal Distribution of Fucus  Some of the earliest studies of Fucus emphasized the role of physical factors in determining the vertical intertidal distribution of Fucus.  Gail (1918) concluded that “light is a controlling factor in  determining the lower limit of Fucus”.  Zanveld (1937) emphasized the  effects of desiccation as a primary controlling factor in intertidal algal zonation which have been re—emphasized recently by Bdrard—Therriault and Cardinal (1973) who stressed the role of desiccation in determining vertical distributions of the Fucaceae.  McLachlan (1974) suggests that  the lack of Fucus in the sublittoral zone could be the result of a lack of colonization by embryos.  Although the ultimate lower limit of Fucus  is probably determined by physical factors, the potentially realized lower distribution in the intertidal zone is determined by biological inter actions.  No single factor however, can be said to be responsible for a  noted distribution but rather, more than one factor may be operating in one area.  Those major factors which seem to control, in part, the lower  limits of Fucus on Bowen Island and Point Atkinson are as follows: (1)  Pisaster—induced mortality.  As my field and laboratory results have  shown, Pisaster can, through predatory activity on those barnacles to which fucoids are attached, disengage the plants from their substrate which results in death to the removed plants.  The upper limits of Pisaster  migration coincides remarkably with the lower limits of Mytilus edulis and  52 the Fucus zone.  Barnacles, B. glandula, in the lower intertidal zone  did not attain a size greater than two or three millimeters in diameter presumably because of repeated predation by Pisaster.  Above the Pisaster  zone barnacle sizes vary from newiy settleu forms to large (5—6 mm in diameter) forms suggesting an age class distribution from one to a few years. (2)  Competitive inhibition by Mytilus edulis.  Mytilus can kill Fucus  by smothering or by removing the entire plant from its substrate.  As the  field experiments have shown, the growth of Fucus is effectively curtailed through the smothering effect of Mytilus.  The ability of N. ëdulls to  crawl CHarger, 1970) gives the mussel a competitive advantage over permanently attached forms such as Fucus.  Mytilus may cause mortality  to Balanus glandula by overcrowding and eventually suffocating them (Ross and Goodman, 1974). (3)  Grazing by Pagurus.  Most species of intertidal hermit crabs are  generalized feeders, feeding on a variety of dead and decaying plants and animals (Vance, 1972).  On Bowen Island Pagurus assumes the role of a  hervivore for at least part of the year and effectively reduces the growth of Fucus in the lower intertidal zone.  Field and laboratory experiments  show that Pagurus can extensively graze on Fücus, primarily the juvenile forms.  Such grazing can either retard growth or kill small fucoids.  An  interesting unanswered question concerning hermit crab grazing is why grazing is only prominent in the late summer months.  One possible reason  may be the result of seasonal differences in aspects of the biochemistry of the plant which renders it more palatable in late summer.  A second  possibility may be that the end of summer marks the end of preferred food  53 sources of the hermit crab such that the animal is forced to feed on Fucus.  c)  Such hypotheses require further investigation.  Fucus Characteristics at Bowen Island and Lighthouse Park  The differences in characteristics of plants from Lighthouse Park and Bowen Island may be the result of differences in the degree of exposure between the two sites.  Increased wave action has been shown  to decrease vesiculation in Fucus vesiculosus and decreased salinity to increase vesiculation and branching (Jordan and Vadas, 1972).  Surf  strength and current speed significantly affected the growth and development of fucoids of the White Sea, with plants growing on sites with a strong surf being longer and structurally stronger (Terekhova, 1972).  Knight and Parke (1950) suggest that exposure to rough water  may accelerate dichotomy of F. serratus.  The increased wave action at  Lighthouse Park may account for the larger size and greater number of dichotomies found than at Bowen Island.  To validate this hypothesis  controlled transfer experiments are required.  The presence of an upper  intertidal form which is reproductive in winter on Bowen Island is similar to the situation on the Atlantic Coast where F. edentatus and and F. distichus form mature receptacles during winter (McLachlan, 1974).  54  SUNMARY  Intertidal Fucus populations at Bowen Island and Lighthouse Park have an associated faunal community which varies seasonally in terms of the abundance of organisms and the diversity of the animal assemblage as expressed by the indices (H’) and (H).  Multiple regression  analysis indicated that the degree of algal dichotomization is associated with a considerable portion of the yearly variation in animal species diversity.  When analyzed on a seasonal basis, different variables are  more strongly correlated with species diversity at certain times of the year.  These variables are plant height diversity, quadrat position,  mean number of dichotomies per plant and mean height per plant. Differences in animal species diversity observed between the two study sites may result from differences in algal structure, algal palatability, the degree of wave exposure, the type of substrate on which the plants are attached, and competitive exclusion processes.  Biological interactions were found to control, in part, the lower intertidal distribution of Fucus. (1)  These interactions include:  Predatory activity by Pisaster ochraceus on barnacles to which plants are attached which results in plant mortality.  (2)  Seasonal grazing by hermit crabs which kills plants or reduces their growth.  (3)  Competition for space with Mytilus edulis which results in the smothering and eventual death of Fucus plants.  55  LITERATURE CITED Bayne, B.L. 1965. Growth and delay of metamorphosis of the larvae of Mytilus edulis. Ophelia 2(1): 1—47. Behrens, S. 1971. The distribution and abundance of the intertidal prosobranchs Littorina scutulata (Gould 1849) and L. sitkana (Phillipi 1845). M.Sc. Thesis, Dept. of Zoology, University of British Columbia. Importance de certains B&rard—Therriault, L. and A. Cardinal. 1973. la dessication des facteurs co1ogiques sur la resistance Fucaces (Phaeophyceae). Phycologia 12(½): 41—52. Bousefield, EL. 1957. Ecological investigations on shore invertebrates of the Pacific coast of Canada, 1955. Nat. Ntis. Can. Bull. No. 147: 104—115. Science and information theory. Brillouin, L. 1962. New York: Academic Press.  d. ( n 2  ed.),  Burrows, E.M. and S. Lodge. 1951. Autecology and the species problem in Fucus. J. Mar. Biol. Ass. U.K. 30: 161—176. Chapman, A.R.O. 1973. A critique of prevailing attitudes towards the control of seaweed zonation on the seashore. Botanica Marina 16: 80—82. Colman, J.A. 1939. On the faunas inhabiting intertidal seaweeds. J. Mar. Biol. Ass. U.K. 24: 129—183. Connell, J.H. l96la. Effects of competition, predation by Thais lapillus, and other factors on natural populations of the barnacle Balanus balanoides. Ecol. Monogr. 31: 61—104. Connell, J.H. l961b. The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42: 710—723. Connell, J.H. 1970. A predator—prey system in the marine intertidal region. I. Balanus glandula and several predatory species of Thais. Connell, J.H. 1972. Community interactions on marine rocky intertidal shores. Ann. Rev. Ecol. and Syst. 31: 169—192. Dawson, E.Y. 1961. A guide to the literature and distributions of Pacific benthic algae from Alaska to the Galapagos Islands. Pacific Science 15: 370—461. Dayton, P.K. 1971. Competition, disturbance, and community organization: The provision and subsequent utilization of space in a rocky intertidal community. Ecol. Monogr. 41: 351—389.  56 Fritsch, F.E. 1945. The structure and reproduction of the algae, Cambridge: Cambridge University Press. 939 pp. vol. 2. Some experiments with Fucus to determine the factors Gail, F.W. 1918. controlling its vertical distribution. Publ. Puget Sound Biol. Sta. 2: 139—151. Glynn, P.W. 1965. Community composition, structure, interrelationships in the marine intertidal Endocladia muricata—Balanus glandula Beaufortia 12(148): 1—198. association in Monterey Bay, California. Haage, P. and B. Jansson. 1970. Quantitative investigations of the Baltic Fucus belt macrofauna. 1. Quantitative methods. Ophelia 8: 187—195. Hagerman, L. 1966. The macro— and microfauna associated with Fucus serratus L., with some ecological remarks. Ophelia 3: 1—43. Harger, J.R.E. 1970. The effect of species composition on the survival of mixed populations of the sea mussels Mytilus californianus and Mytilus edulis. The Veliger 13: 147—152. Harger, J.R.E. 1972. Competitive coexistence among intertidal invertebrates. Amer. Sci. 60: 600—607. Harger, J.R.E. and K. Tustin. l973a. Succession and stability in biological communities. Part 1: Diversity. Intern. J. Environ. Studies 5: 117—130. Harger, J.R.E. and K. Tustin. l973b. Succession and stability in biological communities. Part 2: Organization. Intern. J. Environ. Studies 5: 183—192. Hill, M.O. 1973. Diversity and evenness: A unifying notation and its consequences. Ecol. 54: 427—432. Hurlbert, S.H. 1971. The nonconcept of species diversity: A critique and alternative parameters. Ecol. 52: 577—586. Institute of Oceanography, University of British Columbia, 1970. Data Report 30. British Columbia Inlets and Pacific Cruises 1969. 65 pp. Institute of Oceanography, University of British Columbia, 1973. Data Report 34. British Columbia Inlets and Pacific Cruises 1972. 95 pp. Jaffe, L.F. 1968. Localization in the developing Fucus egg ánd the general role of localizing currents. Adv. Morph. 7: 295—328. Janzen, D.H. 1969. and dispersal.  Seed—eaters versus seed size, numbers, toxicity Evol. 23: 1—27.  57 Jones, N.S. 1948. Observations and experiments on the biology of Patella vulgata at Port St. Mary, Isle of Man. Proc. Trans. Liverpool Biol. Soc. 56: 60—77. Jordan, A.J. and R.L. Vadas. 1972. Influence of environmental parameters on intraspecific variation in Fucus vesiculosus. Mar. Biol. 14: 248—252. Knight, N. and M. Parke. 1950. A biological study of Fucus vesiculosus L., and F. serratus L. J. Mar. Biol. Ass. U.K. 29: 439—514. Lewis, J.R. 1964. The ecology of rocky shores. Universities Press. 323 pp.  London: English  Levin, D.A. 1971. Plant phenolics: An ecological perspective. Am. Nat. 105: 157—181. Lodge, S.M. 1948. Algal growth in the absence of Patella on an experimental strip of foreshore, Port St. Mary, Isle of Man. Proc. Trans. Liverpool Biol. Soc. 56: 78—85. MacArthur, R.H. 1958. Population ecology of some warblers of Northeastern coniferous forests. Ecol. 39: 599—619. MacArthur, R.H. 1965. Rev. 40: 510—533.  Patterns of species diversity.  Biol.  Mann, K.H. 1972. Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. II. Productivity of the seaweeds. Mar. Biol. 14: 199—209. Mann, K.H. 1973. Seaweeds: Their productivity and strategy for growth. Science 182: 975—981. McLachlan, J. 1974. Effects of temperature and light on growth and development of embryos of Fucus edentatus and F. distichus ssp. distichus. Can. J. Bot. 52: 943—951. McLachlan, J., L.C—M. Chen, and T. Edeistein. 1971. The culture of four species of Fucus under laboratory conditions. Can. J. Bot. 49: 1463—1469. Murdoch, W.W., F.C. Evans, and C.H. Peterson. 1972. Diversity and pattern in plants and insects. Ecol. 53: 819—829. North, W.J. 1964. Experimental transplantation of the giant kelp, Macrocystis pyrifera. Proc. 4th. mt. Seaweed Symp., p. 248—254. Pace, D.R. 1972. Polymorphism in Macrocystis integrifolia Bory in relation to water motión. M.Sc. Thesis, Dept. of Botany, University of British Columbia. Paine, R.T. 1966. Food web complexity and species diversity. Am. Nat. 100: 65—75.  58 Paine, R.T. 1971. A short term experimental investigation of resource partitioning in a New Zealand rocky intertidal habitat. Ecol. 52: 1096—1106. Pianka, E.R. 1967. On lizard species diversity: North American flatland deserts. Ecol. 48: 33—351. Pielou, E.C. 1966. Species diversity and pattern diversity in the study of ecological succession. J. Theoret. Biol. 10: 370—383. Pollock, E.G. 1969. Interzonal transplantation of embryos and mature plants of Fucus. Proc. 6th. mt. Seaweed Symp., p. 345—356. Powell, H.T. 1963. Speciation in the genus Fucus L., and related genera. In: Speciation in the sea. Systematics Association Publ. No. 5, Làndon. p. 63—77. Ross, J.R.P. and D. Goodman. 1974. Vertical intertidal distribution of Mytilus edulis. The Veliger 16: 388—395. Scagel, R.F. 1959. The role of plants in relation to animals in the marine environment. 20th. Ann. Biol. Colloquium, Oregon State College, Corvallis, p. 11—29. Seed, R. 1969. The ecology of Mytilus edulis L. (Lamellibranchiata) on exposed rocky shores. I. Breeding and settlement. Oecologia 3: 277—316. Shannon, C.E. 1948. A mathematical theory of communication. Syst. Tech. J. 27: 379—423.  Bell  Southward, A.J. 1964. Limpet grazing and the control of vegetation on rocky shores. In: Grazing in terrestrial and marine environments. D.J. Crisp ed., Oxford: Blackwell, p. 265—273. Stebbing, A.R.D. 1973. Competition for space between the epiphytes of Fucus serratus L. J. Mar. Biol. Ass. U.K. 53: 247—261. Terekhova, T.K. 1972. Effect of surf strength and current speed on the development of White Sea fucoid algae. Hydrobiological Jour. 8: 13—18. Vadas, R.L. 1968. The ecology of Agarum and the kelp bed community. Ph.D. Thesis, Dept. of Botany, University of Washington. Vance, R.R. 1972. Competition and mechanisms of coexistence in three sympatric species of intertidal hermit crabs. Ecol. 53: 1062—1074. Waaland, J.R. 1973. Experimental studies on the marine algae Iridaea and Gigartina. J. exp. mar. Biol. Ecol. 11: 71—80.  59 Waldichuk, M., J.R. Markert, and J.H. Meikle. 1968. Fraser River Estuary, Burrard Inlet, Howe Sound, and Malaspina Strait Physical Volume II, September and Chemical Oceanographic Data, 1957—1966. 1962 to July 1966. J. Fish. Res. Bd. Canada Manuscript No. 939, 277pp. Widdowson, LB. 1973. The marine algae of British Columbia and Northern Washington: Revised list and keys. Part I. Phaeophyceae (brown Syesis 6: 81—96. algae). Wieser, W. 1952. Investigations on the microfauna inhabiting seaweeds on rocky coasts. IV. Studies on the vertical distribution of the f.auna inhabiting seaweeds below the Plymouth Laboratory. J. Mar. Biol. Ass. U.K. 31: 145—174. Woolf, C.M. 1968. Co. 359 pp.  Principles of biometry.  Toronto:’D. Van Nostrand  Zanveld, J.G. 1937. The littoral zonation of some Fucaceae in relation to dessication. J. Ecol. 25: 431—469.  60  Figure 1 Map of Bowen Island showing study area.  62  Figure 2 Map of Point Atkinson showing study area at Lighthouse Park.  63  64  Figure 3 Diagrammatic representation of Fucus attachment to a cement block.  Ln  “C  66  Figure 4 Experimental cages used in littorinid and limpet growth experiments.  67  n  I -  t;4  —  b:  --I  68  Figure 5 Experimental apparatus used in laboratory experiments with Littorina and Acmaea.  I  —-  acIwn  69  70  Figure 6 Frequency distribution of plants heights at Bowen Island (a) and Lighthouse Park (b).  I -1  H  m  I  In  C  C  or  NO. OF PLANTS  0•  ‘1  C, I -1  H  rq  I  U.)  C  C  (0  NO. OF PLANTS  72  Figure 7 Frequency distribution of number of dichotomies per plant at Bowen Island (a) and Lighthouse Park (b).  .1 • I  I  dO  IT1  SINV1d  I  I  -ON  I  Lf  E  0  8  -2  a  .uj a  .0  z -J 0 Ed a Lfl  Ed 1-4  a a I U I-I  C  -  S.LNV1d  dO  -ON  I  z  -J 0  ILl 0  In ILl  1-4  D I— C I f-i  1-4  C  74  Figure 8 (a)  Regression of Fucus height against number of dichotomies at Bowen Island.  (b)  Regression equation: Y  =  0.132 + 0.344X  Regression of Fucus height against number of dichotomies at Lighthouse Park.  Regression equation: Y  =  0.213 + 0.296X  Comparison of the slopes of the two regression lines yielded a significant difference at  p=O.O5  (F6.l4) and comparisons  between adjusted means at X=7.385 yielded significant differences at pO.OO1 (F=15.97).  T1  I  H  G)  In r m z  C  C  ‘C  X  ‘C  X  XX ‘C  ‘C  ‘C  ‘C  ‘C  DICHOTOMIES  X  (SQLURERDDT)  x  I  H  m z  I  v-i  C  n  -9  ‘C  ‘C  ‘C  ‘C  X  ‘C ‘C  XX  ‘C  DICHOTOMIES  XX  X  X  (SQUARERWT)  cJl  76  Figure 9 (a)  High intertidal form of Fucus from Bowen Island, reproductive January, 1974.  (b)  Mid intertidal form of Fucus from Bowen Island, reproductive, July, 1974.  F,  Ct  0  S  78  Figure 10 Diagrammatic representation of an individual Fucus plant attached to Balanus glandula with some of the most common invertebrates found associated with the alga.  44  79  4 L co  l.Iye  u,oSa  JA.4-ez.  4; 1 t  •Nf.  1j  80  Figure 11 Changes in the number of Littorina sitkana on Fucus per quadrat, Bowen Island, from May 1973 to late July 1974, (a), and Lighthouse Park, (b).  Each sampling interval represents approximately  1.1 months for this and all subsequent plots of this type.  The  curve represents a third order polynomial fitted by the method of least squares.  81  i3D.cO  (a)  x  .<  12J.cXJ  <  ilO.cO x  im.aj  X  Lfl  93.03  c  I—  70.cO  I—  X -  X  5j.O  x x  X  x  x  410.03  xx x  ciJqj z  0.03 0.0  i.0  2.0  3.0  MAY’73  4.0  5.0  E.O  7.0  8.0  S.D  10.0  OCT.’73  1.1.0  12.0  13.0  APR.’74  SAMPLINL INTERVAL  1.4.0 JUL.’74  (,1))  33.03  x  .0O I— I-1  U.,  -4  I -4  -J I.. CD  10.03  x  ‘C x uJ x  Q.03  XIX  0.0 MAY’73  1.0  2.0  3.0  4.0  5.0 SEPT.’73  I.  G.O  7.  SAMPLING INTERVAL  8-0  S.O  10.0  11.0  1.2.0  13.0 JUL.’74  82  Figure 12 Changes in the number of Littorina scutulata on Fucus per quadrat, Bowen Island (a) and Lighthouse Park (b).  83  (a)  -J  x  Lfl  X  La..  x x  bJ  X  X Xt  O4X 0.0  i.0.  X X—t  2.0  x  x  x x x  x  X XQ  30  MAY’73  I  I  4.0  5.0 OCT.’73  6.0  I  7.0  8.0  IX  S.O  10.0  I  I  11.0  12.0  13.0  APR.’74  SAMPLING INTERVAL  i4.0 JUL.’74  (b) X  I  —  9.y3  x U  -J La..  x  3.cyJ  xxx  0. 0.0 MAY’73  1.0  2.0  3.0  4.0  5.0  6.0  7.0  3 SAMP T ERV LITd AL  8.0  9O  10.0  11.0  12.0  13.3 JUL.’7  84  Figure 13 Changes in the number of Mytilus edulis on Fücus per quadrat, Bowen Island (a) and Lighthouse Park (b).  85  (a)  x x  41c0.00  3DOO  x 200.00 i5O.cY3 [000 E0  x x  x  ‘C  0.00 0.0 1.0 MAY’73  2.0  3.0  4.0 5.0 8.0 7.0 8.0 OCT.’73 SAMPLINE3 INTERVAL  9.0  10.0 il.O APR.’74  12.0  13.0  iA.O JUL.’74  (b) 700.00  f-n -4  x  -J CD  50003  u.  ‘C  ‘C  x  400.00 -4  >-  30.00  CD  ‘C Ui  cx  i00O  ‘C  x  0.00 0.0 1.0 MAY ‘73  2.0  3.0  4.0  5.0 SEPT.’73  6.0  7.0  SAMPLING INTERVAL  8.0  9.0  jj.3  12.0  13.0 JUL.’7  86  Figure 14 Changes in the number of aniphipods on Fucus per quadrat, Bowen Island (a) and Lighthouse Park (b).  87  ( a)  x  x 0  x x  C-.  .c  ‘C  75.03  x  x x  ‘C  x  53.03 w  x x x 0.00 1.0  2.0  3.0  4.0  MAY’73  5.0  G.0  8.0  7.0  10.0  -  OCT.’73  SAMPLINt3 INTERVAL  53.03  il.0  2.0  13.0  APR.’74  i4’O JUL.’74  (b)  45.00  43.00  33.00 Li  x  :  a.,’  0.0 MAY’73  ..i  1.0  I  I  2.0  2.0  XI  4.0  5.0  I-  I  I  I  8.0  7.0  8.0  g.  SEPT.’73  SAUPLINI3 INTERVAL  10.0  il.O  12.0  5.3.0 JUL.’74  88  Figure 15 Change in mean species diversity (H’) per quadrat (triangles) and Fucus height diversity (crosses), Bowen Island.  89  2”:  I ‘S  z 4<  w  MAY’73 SAMPLING  INTERVAL  JUL. ‘74  90  Figure 16 Changes in the mean number of animals on Fucus per quadrat at Lighthouse Park (crosses) and Bowen Island (triangles).  91  u-i J  350.  H  z 1<  L I  C a a [ti  MAY’73  JUL.’74  SAMPLING  INTERVAL  92  Figure 17 Regression of species diversity (H’) against Fucus height diversity for Bowen Island.  The regression is significant at  pO.OO1  (F14.33),  and the probability of the slope being zero is less than 0.001.  93  x K XX X  K  >-  x  I-  K K  ,<‘k  H  K  XX  I’)  <x  X K  3  XXX  w  XX X  >  XX  H  K  a In w  X  K  XX  XC K  K  w U)  x  X  K  ‘I  X’  U  x x X  K  H  X K  X K  x x .5  OeO  FUCUS  HEIGHT  DIVERSITY  3.0  (H’)  94  Figure 18 Frequency distribution of numbers of Littorina sitkana on plants at Bowen Island. Plants 0—5 cm in height.  (b)  Plants 5—10 cm in height.  Cc)  Plants 10—15 cm in height.  No. of plants  =  51,  Cd)  Plants 15—20 cm in height.  No. of plants  =  29,  Ce)  Plants  >  20 cm in height.  No. of plants  35.  (a)  =  No. of plants  No. of plants  90.  =  =  7.  In  ‘1  0  r  I 0  C  0  ‘I 2  1) m  2  I.i -I  0  t  r  ii  9  ,  NuMBERS or L.  SZTRANA  e •  CD  0  2 0 r  2 0  n  2  0  OP I..  U  U U  U  U  Ii) •1  -I  U)  U  U U U U  U U  U U  0  2 0 C I  ‘I  n  2  In -I  0  -I  B  ‘I  0  I-  0  C I  ‘I 2 0  m  B  U  —  n m  2  -I  B  0  r  IXTRANA  1Z?IIAWA  C r 0 ‘I  I  C  ‘I 2 0  2  a  CR1  NUMBERS CF,L.  NUh  NUMBERS OF L.  NUMBERS OF L•  SZTANA  5ZTANA  96  Figure 19 Frequency distribution of Hyale plumuibsa on individual plants, Bowen Island. (a)  Plants 0—10 cm in height.  (b)  Plants 10—20 cm in height.  Cc)  Plants > 20 cm in height.  No. of plants No. of plants No. of plants  31.  =  27.  =  5  -4  U,  0 ‘1  r  I 0  0  •7  m  C-,  U, -4 >.  ‘-4  0  m  4--  U)  4-  a)  a)  U!  U,  ru  I  94—) I Lfla) ê I  ‘H  I  “Ca) I  U)  .  Pi  F  NUMRS  I’ I  HAL I  I  1 1  PLUMULSA I I  -  (n  z  1  C-)  z  -I  0  >  -n  0  I-  ,  ‘I  U)  >  o  o  ‘1  rn  z  0  r  ‘-I  tJ,  NUMBERS  NUMBERS  OF  OF  HYALE  HYALE  PLUMULOSA  PLUMLJLOSA  98  Figure 20 Frequency distribution of Mytilus edulis on individual plants, Bowen Island. (a)  Plants 0—5 cm in height.  (b)  Plants 5—10 cm in height.  Cc)  Plants 10—15 cm in height.  Cd)  Plants > 15 cm in height.  No. of plants  24.  =  No. of plants  =  32.  No. of plants No. of plants  35.  =  18.  0  10  —I  0)  >;  —49  •  -5  tn  t•  •  o  ‘I  cj,  H  ri  z  -49  tn  o  1  I  8 I  NUMBERS  NUMBERS  I  OF  I•  OF  M.  I•  M.  I I  LOULZS  bi  EOULIS  I I  I  0.  I  8  C-)  —I  8  Lfl  -4  > U,  ‘1  C  0 r  •1  0 m  -1 >  U)  I-I  C  >;  -I,;  Z  >  -49  H  0  0 UI  NUMBERS  8  NUMBERS  _  OF  OF  M.  M.  EOULXS  I•  COULtS I  I’  8  100  Figure 21 Changes in mean species diversity (H’) of the substrate fauna on Bowen Island (crosses) and Lighthouse Park (triangles).  101  2.  F-’.  3: .1  j  z w  0.  i’  2.  3.  4.  5.  6.  7.  6.  9.  MAY ‘73  ‘a  JUL. ‘74  SAMPLING  INTERVAL  102  Figure 22 Changes in mean species diversity (H’) of structurally different plants transplanted into three different Fucus density zones. (a)  Low density zone.  (b)  Medium density zone.  Cc)  High density zone.  Cd)  All zones combined. +  =  low level of complexity plants  X  =  medium level of complexity plants  =i.high level of complexity plants  -.4  m  ‘-I  -I  In  ‘-4  MEAN  IflAN  (H’)  (H’)  n  —I  Cr’  -I  in  ‘-4  MCAN  MEAN  (H’)  (H’)  C-  a U)  ha  104  Figure 23 Changes in mean species diversity (HT) for groups of plants transplanted into two Fucus density zones, (a)  Low density zone.  (b)  High density zone.  (c)  High and low zones combined.  X  =  groups of more than 10 plants  =  groups of less than 10 plants.  (a)  I  z LU  TIME  (VEEcS)  ( b)  I  z Lu  TIME  CEE3cS  ( c)  I  z Lu]  TIME  (VuEDcS)  105  106  Figure 24 Changes in mean number of organisms on Fucus for groups of plants transplanted into two Fucus density zones. (a)  Low density Fucus zone.  (b)  High density Fucus zone.  X  =  groups of more than 10 plants  =  groups of less than 10 plants  107  (a) Ii) J  ‘-4  z Li  ico.  z U  7-  TIME  (VIEEJcS  .( b) i75. U) I  < iso.  z  i.  tJ  z  75  50. U  5.  2.  TIME  ‘VEBSS)  7.  1.  108  Figure 25 Regression of limpet length against limpet height for limpets under three experimental treatments. (a)  Cages with no Fucus. Original Equation: Y= —0.104 + O.460X Final Equation:  (b)  Y= —0.132 + O.474X  Cages with a plant of medium complexity. Original Equation: Y= —0.325 + O.584X Final Equation:  (c)  Y= —0.108 + O.490X  Cages with a plant of high complexity. Original Equation: Y= —0.135 + O.462X Final Equation:  Y  —0.123 + O.469X  +  =  original length—height relationship  V  =  final length—height relationship  109  (a)  (b)  V  U  i.c  V  V  0.E  +  +  I—  V  ‘-I  i.c  * +  H  0.E  V  4v3 4 4J  V  +  H  -J  ‘F  o.od.s  i.S  0.0 0.0  E.O  05  LIMPET LENGTH (CM)  i.5  2.0.  LIMPET LENGTH (CM)  Cc) V  +  I H  V  0. .5  I jO  j.O  j.5  LIMPET LENGTH (CM)  •  2.5  3.0  110  Figure 26 General pattern of Fucus zonation on Bowen Island.  111  :1’  112  Figure 27 (a)  Photograph of Pagurus—grazed plant from laboratory experiment along with an individual Pagurus.  (b)  Pagurus—grazed plant from the lower intertidal zone, Bowen Island.  114  Figure 28 Regression of Fucus height against growing time for mid intertidal plants (triangles) (Y (crosses)  (Y  =  1.877 + 1.566X) and high intertidal plants  2.606 + l.195X), Bowen Island.  115  b  I— 2:  K  x  I.-’  x x  Li I fJ] D U D Li  4’  3a  JUNE’73  J  S A M P L I N G  A  S  I N T E R,V A L  OCT. ‘73  116  Figure 29 Growth and dichotomization of 10 plants that settled on cement blocks on Bowen Island.  Triangles illustrate the  increase in the number of dichotomies and the crosses show the growth rate.  S3tVOiOH.tcI  .O  ‘ON  ‘W  ChV)  HIMOeI9  I—  w  —I > ILl  z H  z H  -J  a 1r)  118  Figure 30 (a)  Grazing marks from Idothea and an individual Idothea.  (b)  Comparison of grazed plants (left) and ungrazed plants (right) from Bowen Island.  Two individual Idothea can be seen  situated on the plant to the left.  q  611  120  Figure 31 Changes in mean species diversity (H’) per quadrat  (+) and  Fücus height diversity CX) at Lighthouse Park from May, 1973 to July, 1974.  121  3.0  2.QL  I  z 4:  Li  0.0 0. MAY’73  je  2.  .  4.  5.  €3.  SAMPLING  7.  8a  9’ ±0.  jjc  INTERVAL  i3 JUL.’74  j2.  122  Figure 32 Frequency distribution of Mytilus edulis on individual plants from Lighthouse Park. (a)  Plants 0—10 cm in height.  No. of plants  =  44.  (b)  Plants  No. of plants  =  33  >  10 cm in height.  ::  (a)  123  o. 275 n . . 2 J ZI Lii  Li.  175.  iEe.  . 00 WI  D  z so.  6.  7  8.  8.  0.  (b) ax. (fl  75•  I-4  C Lii  Li.  175.  a (J  ISO.  DISTANCE  FROM  HOLOFAST  COAl  10.  124  Figure 33 Mean growth rate of two groups of 6 plants cleared of Mytilus (crosses) and two groups of 6 plants left with their Mytilus complement intact (triangles). (a)  Experiment 1.  (b)  Experiment 2.  s.  125  (a)  i2.  I  I  9.  w U  z [LI  3’  0.. ----r-----f--±--±--+-H--4--H---±0. jO. 20. 3). -40. 50. 50. 70 50. 90X).j10wj2043).j40. -  TIME  (DAYS)  (b)  I  (SI  U L  z w  TIME  (t1AYS)  126  Figure 34 Selection of Fucus plants by Idothea in the laboratory. (a)  10 Idothea per trial  (4 trials combined)  (b)  15 Idothea per trial  (4 trials combined)  Cc)  25 Idothea per trial  (6 trials combined)  C-)  -I  I..  r m x  -U  D  U)  C  ,  9  0  I  NO. OF I’  ZOOTHEA PER I  PLANT  §  ‘1  U)  H  x  r  -U  ly  C  C-,  C Ii,  C  H  x  r  C If)  C  I  0  NO  OF  NO.. OF PR PLANT  tOOTHA PER PLANT  ZOOTHEA  01  128  APPENDIX  Levels of significance for the following tables are indicated as following: N.S. **  =  Not significant  =  p<o.ol  =  p<O.OO1  129  Table 1  Comparisons of structural characteristics of Fucus between Bowen Island and Lighthouse Park  (1)  Mean height per plant Group  Mean  Standard Deviation  Sample Size  Lighthouse Park  8.244  2.835  42  Bowen Island  5.479  2.945  89  (2)  25.763***  Number of plants per guadrat Group  Mean  Standard Deviation  Sample Size  Lighthouse Park  30.125  22.257  42  Bowen Island  38.117  37.571  89  Standard Deviation  Sample Size  (3)  F  F 1.571 N.S.  Number of dichotomies per plant Group  Mean  Lighthouse Park  9.196  8.091  42  Bowen Island  7.315  8.739  89  F 1.387 N.S.  __  Table 2 130  List of organisms found associated with Fucus and on the substrate under Fucus at Bowen Island and Lighthouse Park  ci) 4.J Ct  ci) cii  .—‘  CO  4-) CO  CO  —  C) 3 rx.  tl)  :i  :i  C)  Co Cl)  ‘-‘  a)  ci)  Mytilus edulis  X  X  X  X  Littorina sitkana  X  X  X  X  Littorina scutulata  X  X  X  X  Hyale plumulosa  X  X  X  X  Acmaea pelta  X  X  X  X  X  —  X  Acmaea testudinalis scutum  —  Acmaea persona  —  X  Balanus glandula  X  X  X  X  Chthamalus dali  -  X  -  X  Idothea wosnesenski  X  X  X  X  Pa gurus granisimonus  X  X  X  X  X  X  X  Pa gurus hirsutiusculus  —  —  X  Hemigrapsus oregonensis  X  X  X  X  Hemigrapsus nudus  X  X  X  X  Emplectonema gracile  X  X  X  X  Emplectonema burgeri  X  X  X  X  Eulalia viridis  —  —  X  Garypus sp.  -  —  X  —  -  -  Ototyphlonemertes sp.  X  X  — -  Syllis adamantea  X  X  X  X  Gnorimosphaeroma oregonensis  X  X  X  X  Parasitengona (mites)  X  X  -  X  Trichopteran larvae  X  X  X  X  Halacarinidae (mites)  X  X  Chironomid larvae  — -  X  — —  Notoplana natans  —  Cyclorrhapha (diptera) Staph ylinid beetles Encrusting bryozoans  X  =  Present  —  X  (—)  X  X —  =  X  Absent  X X  -  X X  X  Bowen Island  Lighthouse Park  (10) 5.80 (10) 6.38 (1) 3.71 (4) 3.36 (4) 3.93 (10) 1.76  1 2 3 4 5 6  (7) 2.04 (9) 3.32 (5) 1.60  Number of plants per quadrat Total height of plants per quadrat Total number of dichotomies per quadrat Mean height per plant Number of dichotomies per plant Number of dichotomies/total height of plants  7 8 9 10 11  40.12  23.01  22.63  Regression Sum of Squares (%)  50.70  36.08  29.72  Regression Sum of Squares (%)  Wet weight of Fucus Dry weight of Fücus Cover value (%) Distance along transect Plant height diversity  Rank order of Independent Variables plus % contribution to total sum of squares (6) (8) (7) (5) 10.25 5.15 3.12 1.26 (6) (4) (7) (11) 10.12 4.54 3.47 1.27 (6) (2) (5) (9) 13.79 10.97 6.93 2.44  (Seasonal Data Pooled)  (3) 16.41 (3) 21.02 (2) 41.24  Independent Variable Code (Number in parentheses)  No. of individuals  (H)  (H’)  Dependent Variable  2  No. of individuals  (H)  (H’)  Rank order of Independent Variables plus % contribution to total sum of squares  (Seasonal Data Pooled)  Dependent Variable  1  Relationships between independent variables and dependent variables, species diversity and total numbers of individual organisms, on Fucus  Table 3  132 Table 4 Relationships between independent variables and dependent variables, species diversity and numbers of organisms, on Fucus, Bowen Island. The data has been partitioned into seasonal components. Dependent Variable  Rank order of independent variables plus % contribution to total sum of squares  Regression S.S. (%)  January (H’) (H) No. of individuals  (11) 28.43 (11) 28.36 (10) 12.74  ((7) 17.77 (7) 17.16 (1) 11.60  (8) 12.76 (8) 10.25 (3) 10.15  (10) 31.40 (10) 29.51 (2) 38.24  (7) 27.94 (7) 24.86 (3) 16.88  (3) 6.82 (3) 6.87 (11) 12.67  (5) 22.22 (5) 27.65 (8) 21.68  (1) 4.01 (9) 5.95 (11) 2.89  (2) 3.46 (11) 4.34 (9) 2.39  (10) 14.06 (10) 14.14 (2) 75.26  (9) 11.03 (9) 9.88 (5) 4.26  (5) 9.36 (5) 8.40 (3) 1.95  (4) 78.27 (4) 80.25 (4) 62.38  (11) 14.58 (2) 11.67 (3) 25.82  (3) 6.98 (3) 7.96 (2) 11.66  87.00 85.41 75.49  April-Nay (H’) (H) No. of individuals  89.39 86.69 i 36 88.36  July (H’) (II) No. of individuals  37.85 48.28 30.31  August (H’) (H) No. of individuals  71.05 74.22 91.39  Sept.—Oct. (H’) (H) No. of individuals  99.82 99.87 99.86  Continued...  133 Table 4 (Continued)  Independent Variable Code 1 2 3 4 5 7 8 9 10 11  Number of plants per quadrat Total height of plants Total number of dichotomies Mean height per plant Number of dichotomies per plant Wet weight of Fucus Dry weight of Fucus Cover value (%) Distance along transect Plant height diversity  134  Table 5 Analysis of variance comparison of final heights of Littorinasitkana for three experimental treatments, no Fucus, medium complexity Fucus, and high complexity Fucus, Bowen Island  Standard Deviation  Sample Size  0.699  0.124  22  Medium  0.718  0.085  25  High  0.705  0.101  40  Group  Mean  No Fucus  F 0.232 N.S.  135  Table 6 Analysis of variance comparisons between final heights of mature plants transplanted to three intertidal sites, low, mid, and high intertidal, Bowen Island  Standard Deviation  Sample Size  F  17.900  3.928  3  0.959 N.S.  Mid  21.083  3.917  6  High  20.790  3.073  10  Group  Mean  Low  136  Table 7 Relationships between independent variables and dependent variables, species diversity and numbers of organisms, on Fucus, Lighthouse Park. The data has been partitioned into seasonal components. Dependent Variable  Rank order of independent variables plus % contribution to total sum of squares  Regression S.S. (%)  Spring (H’) (H) No. of individuals  (6) 20.72 (6) 19.52 (9) 25.86  (9) 11.52 (9) 10.25 (8) 17.66  (7) 6.92 (7) 8.84 (6) 15.60  (7) 40.22 (8) 39.02 (2) 71.65  (8) 31.51 (1) 26.46 (4) 9.58  (4) 12.31 (4) 19.55 (1) 7.33  (4) 46.10 (11) 42.42 (1) 36.84  (9) 30.83 (9) 28.30 (4) 36.80  (1) 9.59 (6) 15.41 (11) 15.86  66.38 66.10 76.60  Summer (H’) (H) No. of individuals  99.85 99.95 99.93  Autumn (H’) (H) No. of individuals  98.51 98.61 98.51  Independent Variable Code 1 2 4 6  Number of plants per quadrat Total height of plants Mean height per plant Number of dichotomies/total height of plants  7 8 9 11  Wet weight of Fucus Dry weight of Fucus Cover value (%) Plant height diversity  137  Table 8 Comparison of numbers of Acmaea pelta remaining on cleared and uncleared areas, Lighthouse Park.  Area Experiment 1 Initial No.  Clare4 43  Final No.  Experiment 2 Initial No. Final No.  Experiment 3 Initial No. Final No.  60  8  “c”—value  Uncleared  32 (+ 4 from cleared area) =  4.02**  Cleared  Uncleared  10  10  0  8  Cleared  Uncleared  10  10  0  5  (+ 4 from cleared area)  (+ 6 from cleared area)  138  Table 9 .Analysis of variance comparison of numbers of Littorina sitkana found on Fucus and No—Fucus side of experimental tank after 10 trials  Group  Mean  Fucus  19.80  No Fucus  22.10  Sample Size  F  6.579  10  0.580 N.S.  6.919  10  Standard Deviation  Analysis of variance comparison of numbers of Littorina scutulata found on Fucus and No—Fucus side of experimental tank after 7 trials  Sample Size  Group  Mean  Fucus  22.85  5.815  7  No Fucus  25.85  5.984  7  Standard Deviation  F 0.905 N.S.  139  Table 10 Selection of structurally variable plants by Iddtheawostiesenski N=lO (Four trials combined) Plant Level  Observed  Expected  1  22  8.5  2  6  8.5  3  6  8.5  4  0  8.5  Chi—square  =  30.917***  N=15 (Four trials combined) Plant Level  Observed  Expected  1  40  15  2  9  15  3  1  15  4  0  15  Chi—square  =  72.12***  N=25 (Six trials combined) Plant Level  Observed  Expected  1  98  37.5  2  19  37.5  3  9  37.5  4  2  37.5  Chi—square  =  16l.98***  Level 1  Plants with more than 40 dichotomies  Level 2  Plants with 20 dichotomies  Level 3  Plants with 10 dichotomies  Level 4  Plants with 0—5 dichotomies  


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